Sonic 3 & Knuckles (sonicretro/skdisasm)

Sonic and Tails take off at $680 subpixels per frame (6.5 px/frame) and Knuckles at $600 (6 px/frame); underwater the speeds are $380 and $300. s3k/jump-speed

About: Sonic 3 & Knuckles Jump

{
 "sonic": 1664,
 "knuckles": 1536,
 "sonicWater": 896,
 "knucklesWater": 768
}

As in the earlier games the speed goes along the ground's normal (L23352-L23362).

Cited by: Jump, Sonic 3 & Knuckles

MoveSprite adds $38 subpixels/frame to a falling player's speed, Sonic 1's and Sonic 2's gravity, and underwater the air modes take $28 back. s3k/gravity

About: Sonic 3 & Knuckles Gravity

Value: 56 1/256 px/frame²

Cited by: Gravity, Sonic 3 & Knuckles

With no jump button held, Sonic_JumpHeight cuts a rise faster than 4 px/frame to exactly -$400 (-$200 underwater); a press once the rise is no faster than that starts a shield move instead. s3k/release-cap

About: Sonic 3 & Knuckles Variable jump height

Value: -1024 1/256 px/frame

Cited by: Sonic 3 & Knuckles, Variable jump height

Sonic_Init sets the top speed to $600, the acceleration to $C, and the deceleration to $80 subpixels, the values of Sonic 1 and Sonic 2. s3k/ground-speeds

About: Sonic 3 & Knuckles Running

{
 "top": 1536,
 "accel": 12,
 "decel": 128
}

As in Sonic 2, holding forward keeps a speed already above the top (s2disasm/forward-cap-kept).

Cited by: Running, Sonic 3 & Knuckles

In the air Sonic_ChgJumpDir still adds $18 a frame, but a Sonic already faster than the top speed keeps his speed; Sonic 1 and Sonic 2 pulled him down to it. s3k/air-keep-speed

About: Sonic 3 & Knuckles Air control

Value: 24 1/256 px/frame²

Cited by: Air control, Sonic 3 & Knuckles, Sonic the Hedgehog 2

Sonic 3 & Knuckles keeps Sonic 1's air drag, X speed less X speed shifted right 5 bits while Y speed is from −$400 to −1. s3k/air-drag-same

About: Sonic 3 & Knuckles Air control

{
 "shift": 5,
 "vyFrom": -1024,
 "vyTo": -1
}

Sonic 3 & Knuckles has no grace window after a ledge: Sonic_Jump is called only from the grounded modes. s3k/no-coyote-time

About: Sonic 3 & Knuckles Coyote time

Value: 0 frames

Tails's and Knuckles's jump routines were not traced for this claim.

Cited by: Coyote time, Sonic 3 & Knuckles

The spin dash is Sonic 2's, with the same $200 a press to $800, the same 1/32 decay, and the same release speeds from $800 to $C00. s3k/spindash

About: Sonic 3 & Knuckles Spin dash

[
 2048,
 2176,
 2304,
 2432,
 2560,
 2688,
 2816,
 2944,
 3072
]

Cited by: Sonic 3 & Knuckles, Sonic the Hedgehog 2, Spin dash

Unlike Sonic 1 and Sonic 2, a standing player slides on a slope whose push, sine × $20, is at least $D; the walking and rolling factors stay $20 and $50. s3k/slope-standing

About: Sonic 3 & Knuckles Slope physics

{
 "walk": 32,
 "rollDown": 80,
 "standMin": 13
}

s3.asm has the same branch (L21460-L21468), so Sonic 3 alone slides too. With a sine of 1.0 as 256, $D needs a sine of at least 104/256, an angle of roughly 24° or more.

Cited by: Slope physics, Sonic 3 & Knuckles, Sonic the Hedgehog, Sonic the Hedgehog 2

Below $280 ground speed on a steep slope the player now slips, a $80 push along the slope and a 30-frame d-pad lock, and falls off only near walls and ceilings; Sonic 1 and 2 dropped him from any slope past 45°. s3k/slope-slip

About: Sonic 3 & Knuckles Slope physics

{
 "minSpeed": 640,
 "lock": 30,
 "nudge": 128
}

Angles are bytes, $40 a quarter turn. Sonic 3 & Knuckles checks angles past $18 (about 34°) and drops the player only past $30 (about 68°); Sonic 2 drops him past $20 (45°) and zeroes his speed.

Cited by: Slope physics, Sonic 3 & Knuckles

Rolling keeps Sonic 2's numbers, friction of half the acceleration ($6), $20 more against the d-pad, and X speed clamped to $1000. s3k/roll-speeds

About: Sonic 3 & Knuckles Rolling

{
 "friction": 6,
 "brake": 32,
 "xCap": 4096
}

Cited by: Rolling

Against objects the player is still a 16 px wide box whose half-height is his height radius minus 3, and ducking no longer shrinks it. s3k/hitbox

About: Sonic 3 & Knuckles Hitbox

{
 "w": 16,
 "h": 32,
 "rollH": 22
}

Cited by: Hitbox

A hit throws the player up at -$400 and away from the object at $200 (half both underwater), the speeds of Sonic 1 and Sonic 2. s3k/hurt-knockback

About: Sonic 3 & Knuckles Knockback

{
 "vy": -1024,
 "vx": 512,
 "waterVy": -512,
 "waterVx": 256
}

Cited by: Knockback

The invulnerability count is now a byte but still 120, set by the hit and again on landing, and still blinks the sprite. s3k/hurt-invulnerable

About: Sonic 3 & Knuckles Invincibility frames

Value: 120 frames

Cited by: Invincibility frames

Hit without a shield, the player drops his rings, at most 32 as bouncing rings, and the count goes to 0; with no rings he dies. s3k/hurt-rings

About: Sonic 3 & Knuckles Rings as health

{
 "scatterMax": 32
}

Cited by: Rings as health, Sonic 3 & Knuckles

A hit with any shield costs the shield, not the rings; HurtCharacter clears the shield bit and all three element bits together (`andi.b s3k/shield-loss

About: Sonic 3 & Knuckles Shields

Cited by: Sonic 3 & Knuckles

An elemental shield makes the player immune to each object whose shield_reaction byte names that element, and any shield deflects objects flagged for it at 8 px/frame. s3k/shield-immunity

About: Sonic 3 & Knuckles Shields

{
 "deflectSpeed": 2048
}

Which hazards carry which bits (fire, electric, water, projectile) is set object by object and was not surveyed.

Cited by: Shields, Sonic 3 & Knuckles

A second press during a jump, once the rise is no faster than 4 px/frame (2 underwater), uses the shield: fire dashes at 8 px/frame and stops the fall, lightning jumps again at -$580, and bubble stops dead and drops at 8 px/frame, then bounces at 7.5 px/frame on landing. s3k/shield-moves

About: Sonic 3 & Knuckles Shields

{
 "fireX": 2048,
 "lightningY": -1408,
 "bubbleY": 2048,
 "bubbleBounce": 1920,
 "bubbleBounceWater": 1024
}

Only Sonic gets the moves; Sonic_FireShield is skipped while he is invincible. The bounce goes along the ground's normal.

Cited by: Shields, Sonic 3 & Knuckles

With no shield, the press gives Sonic the insta-shield, which while active makes him invincible and widens his hit box to 48 × 48 px. s3k/insta-shield

About: Sonic 3 & Knuckles Shields

{
 "w": 48,
 "h": 48
}

How many frames the attacking mode lasts is set by the shield object's animation and was not traced.

Cited by: Shields, Sonic 3 & Knuckles

Sonic 3 alone (s3.asm) has the same shield moves and insta-shield; its transformation check asks only for the seven Chaos Emeralds and 50 rings. s3k/sonic-3-alone

About: Sonic 3 & Knuckles Shields

Cited by: Sonic 3 & Knuckles

Tails flies for 480 frames, a count of 240 that drops every other frame; flying adds $8 gravity a frame, and while time remains each press lifts him $20 a frame for up to 30 frames, until he rises faster than 1 px/frame. s3k/tails-flight

About: Sonic 3 & Knuckles Flight

{
 "frames": 480,
 "gravity": 8,
 "lift": 32,
 "liftFrames": 30,
 "liftUntil": -256
}

A press sets the flag to 2; each lifting frame adds 1, and at $20 the lift stops (30 frames). Lifting frames skip the +8. With the count at 0 a press does nothing. Underwater, carrying Sonic, a press doesn't lift.

Cited by: Flight, Sonic 3 & Knuckles

Knuckles's glide starts at 4 px/frame and gains $4 a frame to a cap of 24 px/frame, and its fall settles near 0.5 px/frame, $20 added below $80 and taken above. s3k/knuckles-glide

About: Sonic 3 & Knuckles Flight

{
 "start": 1024,
 "accel": 4,
 "cap": 6144,
 "fallTarget": 128,
 "fallStep": 32
}

The start adds $200 to Y speed and stops any rise. Gliding needs the button held; letting go quarters the X speed and drops him. Turning holds the speed and swings the direction through a sine.

Cited by: Flight, Sonic 3 & Knuckles

With neither Left nor Right held, Sonic_Move takes the current acceleration off a standing or running Sonic's ground speed each frame, stopping at 0, as Sonic 2 does; that is $C out of water and without speed shoes (ground-speeds), and $C for Super Sonic. With the infinite-inertia flag some objects set (bit 7 of status_secondary), it skips the d-pad and the friction both. s3k/ground-friction

About: Sonic 3 & Knuckles Running

Value: 12 1/256 px/frame²

Sonic 3 & Knuckles keeps Sonic 2's skid bug: on flat ground, not mid-flip (flip_type not negative), a reversal skids (stopping animation, facing his motion) when the slowed speed is at least $400 moving right but only $301 moving left, because the angle read overwrites the speed's low byte. s3k/skid-threshold

About: Sonic 3 & Knuckles Running

{
 "right": 1152,
 "left": 897
}

Moving left, the slowed speed with its low byte zeroed is at most −$400 once it is −$301 or less; before the frame, that is −$381 (897). Moving right it needs $400 after the $80 brake, $480 (1152) before.

On the ground the d-pad turns Sonic only when his ground speed is 0 or already that way, and a skid turns him to face his motion; rolling, the same, with no skid; in the air, Left or Right turns him at once unless he jumped from a roll. While the spin dash charges, the d-pad doesn't turn him. On the ground and rolling, the d-pad is skipped altogether while an object holds his controls: move_lock, the infinite-inertia flag (bit 7 of status_secondary), or, rolling, a negative spin_dash_flag (pinball mode). s3k/facing

About: Sonic 3 & Knuckles Running

A balance turns him too (balance).

Standing, Sonic's floor and ceiling sensors sit 19 px above and below his center and 9 px to each side, a 19 × 39 px box; curled up, 14 and 7, 15 × 29 px; his wall sensors sit 10 px to either side. These are Sonic 2's sizes. s3k/collision-box

About: Sonic 3 & Knuckles Hitbox

{
 "w": 19,
 "h": 39,
 "rollW": 15,
 "rollH": 29,
 "radius": {
  "w": 9,
  "h": 19,
  "rollW": 7,
  "rollH": 14,
  "push": 10
 }
}

A sensor at center + radius tests the radius-th pixel out, so the box spans 2 × radius + 1 pixels.

With Down held, neither Left nor Right, and no infinite-inertia flag (bit 7 of status_secondary), Sonic curls into a roll at a ground speed of $100 or more either way, twice Sonic 2's $80; slower than that, unless he stands on an object, he crouches, where Sonic 2 and Sonic 3 alone crouch only from Sonic_Move's standstill branch. s3k/roll-start

About: Sonic 3 & Knuckles Rolling

Value: 256 1/256 px/frame

The crouch is animation 8, which a jump press turns into a spin dash (spindash-controls); with Down released, Player_ChkWalk sets animation 0 again. Holding Left or Right skips the routine, so a crouch already begun stays through a brake.

Cited by: Sonic 3 & Knuckles

Outside pinball mode (spin_dash_flag set on a roll) and without the infinite-inertia flag, a roll ends once friction and the d-pad leave the ground speed under $80 either way, and the speed left is kept; Sonic 2 and Sonic 3 alone unroll only at 0. Standing up moves his center 5 px up with normal gravity. In pinball mode a positive flag sets the speed to $400 in his facing direction instead, and a negative one skips the d-pad, friction, and this check. s3k/unroll

About: Sonic 3 & Knuckles Rolling

Value: 128 1/256 px/frame

The check runs after the roll's friction, every rolling frame. spin_dash_flag stays 0 on a roll in the lab.

Cited by: Sonic 3 & Knuckles

Crouching (animation 8), a press of A, B, or C starts the spin dash's charge at 0; while Down stays held, each frame first takes 1/32 of the counter (rounded down) and a press adds $200, to $800; letting go of Down releases it, curling him (5 px down) and setting the ground speed from the counter's high byte (spindash; Super Sonic's table is faster), negated facing left. On the start, charge, and release frames he doesn't move, and the floor sensors still run. The charge's decay, step, and cap are Sonic 2's. s3k/spindash-controls

About: Sonic 3 & Knuckles Spin dash

{
 "charge": 512,
 "max": 2048,
 "decayShift": 5
}

The crouch can begin while he still moves slower than $100 (roll-start), so a spin dash can start with ground speed left over; it stays until the release sets the speed.

Cited by: Sonic 3 & Knuckles

With room overhead (jump-headroom), a jump press adds the jump speed along the ground's normal, -$680 straight up on flat ground with normal gravity (jump-speed gives the underwater and Super speeds), keeps the X speed, and ends the frame: the jump frame moves nothing. Standing, the jump curls Sonic and moves his center 5 px down (up with reverse gravity); from a roll he keeps the standing size (roll-jump-size). s3k/takeoff

About: Sonic 3 & Knuckles Jump

A jump from a roll sets the roll-jump flag, and while it is set Sonic_ChgJumpDir skips the d-pad: no steering and no turning, though the air drag still runs. Landing clears it, as Sonic 2's Sonic_ResetOnFloor does; unlike Sonic 2, whose Sonic_JumpHeight only caps the rise, a jump press once his rise is no faster than 4 px/frame (2 underwater) clears it too (insta-shield-motion), as in Sonic 3 alone. s3k/roll-jump-lock

About: Sonic 3 & Knuckles Air control

A jump from a roll resets Sonic's sensors to the standing size, 19 px below his center, while his ball stays drawn, so he lands 5 px higher than a standing jump would, and landing moves him by the difference, 0. Sonic 2 has the same order of instructions. s3k/roll-jump-size

About: Sonic 3 & Knuckles Jump

Value: 5 px

A jump press during a jump, once the rise is no faster than 4 px/frame (2 underwater) and before any shield move or insta-shield this jump, clears the roll-jump flag before the shield checks, so a roll jump gets its steering back. With no shield, not invincible, not Super, and short of turning Super (50 rings, Update_HUD_timer nonzero, and seven Super Emeralds, or seven Chaos Emeralds with Emeralds_converted_flag clear), the insta-shield follows and doesn't change his position or speed; with an elemental shield its move follows (shield-moves). Later presses do nothing until he lands. s3k/insta-shield-motion

About: Sonic 3 & Knuckles Shields

Sonic 3 alone has the same bclr. The elemental shields' moves do change his motion (shield-moves) but aren't in the lab.

Landing on flat ground keeps Sonic's horizontal speed as his ground speed, sets his Y speed to 0, and, if he was curled and spin_dash_flag is clear (not pinball mode), uncurls him; with normal gravity a ball from a standing jump or a roll moves 5 px up, one from a roll jump doesn't move. It clears the jump, roll-jump, and insta-shield flags; with the bubble shield used, it bounces him instead (shield-moves). s3k/landing

About: Sonic 3 & Knuckles Jump

The lab's stages are built of Angel Island Act 1's block 1, a full 16 × 16 px block solid from every side; Sonic 3 & Knuckles's level collision is 16 × 16 px blocks, and a sensor's search looks in its block and at most one more. s3k/collision-blocks

About: Sonic 3 & Knuckles Hitbox

{
 "word": 61441,
 "index": 255
}

A chunk word's low 10 bits are the block and bits 12 to 15 its solidity for the two collision paths; $F001 is block 1 solid from every side on both. The lab's ROM check reads block 1's collision index in RAM at the start of each run.

On a flat floor, not standing on an object, after each ground move, Player_AnglePos reads two floor sensors, at his center's X ± his width radius and his center's Y + his height radius; the nearer floor counts, and from 1 to 14 px into it he moves up to its surface. s3k/floor-sensors

About: Sonic 3 & Knuckles Hitbox

Above the floor, walk-off decides between a snap down and a fall.

On flat ground, not on an object, when both floor sensors find the floor more than |X speed's high byte| + 4 px below, at most 14, Sonic leaves the ground with his speeds as they are, unless stick_to_convex is set; closer than that, he moves down to it. Sonic 2 has the same rule; Sonic 1 used a flat 14 px. s3k/walk-off

About: Sonic 3 & Knuckles Coyote time

{
 "add": 4,
 "max": 14
}

stick_to_convex, which skips the test, is 0 in the lab.

Cited by: Sonic 3 & Knuckles

Outside Competition mode, on flat ground with a ground speed, Sonic's wall sensor sits 10 px ahead of where the frame's speeds would put his center and 8 px below it; in the air his side sensors sit 10 px to either side of his center at its height. s3k/wall-sensors

About: Sonic 3 & Knuckles Hitbox

Value: 8 px below his center, on flat ground

On flat ground, with a ground speed and bit 6 of object_control clear (no object carrying him), a wall at the sensor ahead cuts the frame's X speed by the sensor's depth in whole pixels, so the move stops him beside it, and sets the ground speed to 0. s3k/ground-wall

About: Sonic 3 & Knuckles Hitbox

In the air SonicKnux_DoLevelCollision picks one of four checks by the direction of his speeds after gravity, from GetArcTan less $20: mostly down, mostly up, mostly left, or mostly right. The arctangent table puts the split where the smaller speed is 250/256 of the larger. s3k/air-quadrant

About: Sonic 3 & Knuckles Hitbox

Value: 250 /256, the ratio of the smaller speed to the larger at which the table reaches `$20`

With both speeds 0, GetArcTan returns $40, the down check.

Moving mostly down or up, both side sensors push Sonic out of a wall and stop his X speed; moving mostly left or right, only that side's does, and it also sets his ground speed to his Y speed. Unlike Sonic 2, a push moving left or right doesn't end the checks: the ceiling and then the floor are still tested. s3k/air-wall

About: Sonic 3 & Knuckles Hitbox

s3.asm's Player_HitLeftWall is the same, so Sonic 3 alone changed this already.

Sonic's head sensors are read in the air only while he moves mostly up, left, or right. Inside a ceiling he moves down by the depth; moving up under a flat ceiling his Y speed becomes 0, moving sideways only if he was rising, and the floor isn't tested that frame. Moving mostly left, a head 20 px or more inside a ceiling is instead pushed off a wall on his right, a check Sonic 2 lacks. s3k/air-ceiling

About: Sonic 3 & Knuckles Hitbox

{
 "tall": 20
}

A ceiling block whose angle is steep lands him on it instead (loc_120EA); the lab's full block has the flat angle.

Falling mostly down, Sonic lands when a floor sensor is inside the ground unless both are deeper than his Y speed's whole pixels plus 8, and moves up by the deeper one's depth; moving mostly left or right and not rising, any depth lands him; rising, he doesn't land, except in a wind tunnel. s3k/landing-depth

About: Sonic 3 & Knuckles Jump

Value: 8 px

The test compares bytes.

Standing on flat ground, not on an object, not Super or Hyper, with no move_lock or infinite-inertia flag, with ground speed 0 after the left and right steps, and the floor under his center 12 px or more below his feet, Sonic turns to face right if last frame's right floor sensor met no block, or else left if the left one met none, and balances; otherwise Down crouches. Sonic 2 turned him only if the floor 6 px back the other way was also that far down. s3k/balance

About: Sonic 3 & Knuckles Hitbox

Value: 12 px

Player_AnglePos writes 3 to both angle buffers and a sensor that meets a block overwrites its own; Sonic_Control copies them to next_tilt and tilt. The edge check here runs on the frame's start position.

Cited by: Sonic 3 & Knuckles

Standing or rolling on flat ground with normal gravity, a jump press goes through only when the head sensors find 6 or more clear pixel rows above them; refused, the rest of the ground frame runs. On slopes and walls, and with reverse gravity, the sensors used turn with the angle. s3k/jump-headroom

About: Sonic 3 & Knuckles Jump

Value: 6 px

CalcRoomOverHead writes $80 to both angle buffers, which the balance check reads the next frame.

On the ground, while Background_collision_flag is clear, nothing but a jump press looks above Sonic: walking or rolling under a block that overlaps him, he stays on the ground. s3k/ground-no-ceiling

About: Sonic 3 & Knuckles Hitbox

Sonic dies once his Y position is more than 224 px below the level's bottom boundary, unless the level has set Disable_death_plane; with reverse gravity it is the top boundary instead. In Angel Island Act 1, run in MAME, every one of 18 falls into a pit killed him on the first frame after his center passed the boundary plus 224 px; the other branches are read in the code only. s3k/bottom-boundary

About: Sonic 3 & Knuckles Fall damage

Value: 224 px

It runs in every mode before the move, so the death comes the frame after his center passes the line. The same routine stops him at the camera's left limit plus 16 px and its right limit plus 296.

A frame-by-frame model of Sonic_MdNormal, Sonic_MdRoll, Sonic_MdJump, and SonicKnux_Spindash on flat ground, with the insta-shield, matches Sonic 3 & Knuckles itself, run in MAME with Sonic alone on a floor built of Angel Island Act 1's blocks, on every frame of the movement lab's flat-ground presets, stress scripts, and spin-dash and roll scripts and of 100 random input scripts. s3k/movement-rule

About: Sonic 3 & Knuckles Running

{
 "ground": {
  "accel": 12,
  "friction": 12,
  "decel": 128,
  "top": 1536,
  "flip": 128
 },
 "roll": {
  "start": 256,
  "stop": 128,
  "friction": 6,
  "decel": 32,
  "flip": 128,
  "cap": 4096
 },
 "air": {
  "accel": 24,
  "top": 1536,
  "dragShift": 5,
  "dragFrom": -1024
 },
 "jump": {
  "speed": -1664,
  "releaseCap": -1024,
  "gravity": 56,
  "rollShift": 5
 },
 "spindash": {
  "charge": 512,
  "max": 2048,
  "decayShift": 5
 }
}

One frame, out of water, g the ground speed and vx, vy the X and Y speeds in 1/256 px/frame, positions 16.16. Down is +y. A, B, or C going down this frame is a press, even with another held. Standing: crouching (animation 8), a press starts the spin dash, and while it charges each frame takes 1/32 of the counter and a press adds $200 (to $800); letting go of Down releases it (curl, Y + 5, g from spindash, negated facing left). These frames, and the start, don't move him. Otherwise a press sets vy −= $680, curls him (Y + 5) unless he is rolling (then the roll-jump flag), and ends the frame. Then Left, then Right: Left with g ≤ 0 faces left and takes $C, a speed past −$600 kept; Left with g > 0 takes $80 (to −$80 if it crosses), skidding (facing right) if the result's high byte is ≥ 4. Right mirrors it, skidding if the result with its low byte cleared is ≤ −$400. With g 0 after them: balance or, with Down, crouch. With neither held, friction $C toward 0. vx = g; with Down and neither Left nor Right, |g| ≥ $100 curls him into a roll (Y + 5), slower crouches. Rolling: Left or Right brake by $20 against the motion (to ∓$80 if it crosses), friction 6, then under $80 he stands up (Y − 5) with g kept; vx is g clamped to ±$1000. Then X += vx and the floor sensors snap him, or he walks off. Air: a jump rising faster than $400 with no button held is cut to −$400; once no faster, the first press clears the roll-jump flag (the insta-shield). Unless roll-jumping, Left and Right add $18 and face that way, a speed past $600 kept. If −$400 ≤ vy < 0, vx −= vx >> 5. X += vx, Y += vy, vy += $38; then the level checks, and landing makes g = vx, vy = 0, and uncurls him (Y − 5 unless roll-jumping). The values: ground-speeds, ground-friction, skid-threshold, roll-start, unroll, roll-speeds, air-keep-speed, air-drag-same, jump-speed, release-cap, gravity, takeoff, spindash, spindash-controls. Slopes, water, objects, and the camera are outside the model.

Cited by: Sonic the Hedgehog

On stages built in Angel Island Act 1 from the act's full 16 × 16 block, the movement lab's Sonic 3 & Knuckles model matches the game itself, run in MAME, on every frame of 100 random stages with random input scripts, three in four with floating blocks, and of the lab's stage presets, until a fall into a pit kills him at the bottom boundary or he nears the end of the built floor. s3k/stage-rule

About: Sonic 3 & Knuckles Hitbox

{
 "stages": 100,
 "frames": 300
}

The stages are Sonic the Hedgehog's layouts (s1disasm/stage-rule), so the two games' runs meet the same walls, ledges, and ceilings, and the camera's limits the probe writes each frame (left 0, right $4000, bottom $300) keep the level's own from moving.

On flat ground, Sonic 3 & Knuckles changes when Sonic rolls and stands: Down curls him only from $100, not Sonic 2's $80, and, off objects, crouches him while he is still moving slower, where Sonic 2 crouched only from a standstill; a roll stands up under $80 with that speed kept, where Sonic 2's rolls on to 0 (both outside pinball mode). In the air he keeps a speed above the top while steering, where Sonic 2 pulled him down to it; a second press after a roll jump gives back steering, which Sonic 2's jump never did; a wall push moving sideways no longer ends the frame's checks; and a head 20 px into a ceiling moving left is pushed off a right wall instead, a check Sonic 2 lacks. Standing over a drop, not Super, he turns toward it at once, where Sonic 2 turned only if the floor 6 px the other way was also low. s3k/movement-differs-from-sonic-the-hedgehog-2

About: Sonic 3 & Knuckles Running

Rules that stayed, each in a claim that quotes Sonic 2's lines beside these: ground-speeds, ground-friction, skid-threshold, roll-speeds, spindash-controls, collision-box, walk-off, and roll-jump-size. Off flat ground there is more: a standing player slides on slopes (slope-standing) and slips rather than falls off steep ones (slope-slip). Sonic 3 alone (s3.asm) already has the air-wall and ceiling change (air-wall, and the s3.asm lines here), the insta-shield's unlock (roll-jump-lock), the turn on a ledge (balance), and the air steering (air-keep-speed), but keeps Sonic 2's roll start at $80, its unroll at 0, and its standstill-only crouch (roll-start, unroll).

Cited by: Sonic the Hedgehog, Sonic the Hedgehog 2

Built at the pinned commit with its own build scripts, as they stand (FixBugs = 0, Sonic 3 Complete off), skdisasm reproduces the No-Intro Sonic & Knuckles + Sonic The Hedgehog 3 (USA) ROM byte for byte: buildSK.lua (sonic3k.asm) gives its first 2 MB, the code the locked-on game runs, and buildS3.lua (s3.asm) its last 2 MB. s3k/rom-matches-build

{
 "sk": "88d6499d874dcb5721ff58d76fe1b9af811192e3",
 "s3": "75e9c4705259d84112b3e697a6c00a0813d47d71"
}

So every s3k claim's code is what the cartridge holds, not a revision near it (contrast Sonic 2, s2disasm/rom-matches-revision-2). The MD5s the repository's chkbitperfect.lua expects of the two builds are these halves' (sonic-3-and-knuckles-genesis-rom).