Metroid II: Return of Samus

On this page

Related
Mechanics
References
Sources

The atlas reads Metroid II: Return of Samus through alex-west’s M2RoS disassembly, which reassembles the World release byte for byte¹. Labels and comments cited here are the disassembly’s. Nothing here has been measured in the ROM yet.

Samus’s jump has no gravity. While A is held, she rises at a fixed 2 px per frame for up to 15 frames, or 3 px for up to 31 with the Hi-Jump Boots². A table then moves her a whole number of pixels each frame through the top of the arc and the fall³. She walks at a steady 1.5 px per frame, and the Varia Suit raises it to 2⁴.

A hit gives 51 frames⁵ of invincibility⁵ and throws Samus along a fixed arc away from the enemy⁶. A jump press during that arc starts a jump in midair and ends the invincibility⁷.

Samus can roll into the morph ball from the start⁸, and the Spring Ball lets the ball jump⁹. The Space Jump restarts a spin jump at a new press, but only during part of the fall¹⁰.

Mechanics

Mechanic	Kind	How
Jump	Table	a held linear rise, then one pixel step per frame from a 79-entry table
Variable jump height	Hold timer	A holds a 2 px/frame rise for up to 15 frames, 31 at 3 px/frame with the Hi-Jump Boots
Running	Instant	1.5 px/frame from 1- and 2-pixel steps, 2 px/frame with the Varia Suit
Air control	Direct	1 px/frame toward a held direction in a plain jump, none without
Hitbox	Points and a box	up to five points per side against the background, a box against enemies
Invincibility frames	Frame timer	a 51-frame timer that drops each time Samus is drawn
Knockback	Table arc	a fixed arc from its own table, 3 px/frame up and 1 sideways, which a jump press cancels
Health upgrade	Whole containers	up to 5 energy tanks, each one refilling her energy
Ammunition	One pool	30 missiles at the start, 10 more per missile tank, up to 999
Morph ball	Spring upgrade	available from the start; the Spring Ball lets it jump
Space Jump	Window in the arc	a new press restarts a spin jump during 20 entries of the arc's fall
Screw Attack	Any spin	any spin jump, from its start pose
Status bar split	Window layer	the HUD is the window's bottom 8 lines, raised to 16 for save and item messages; the Queen's head takes the window in her room
Gravity	None	no gravity in a jump; the arc table sets every frame's step
Coyote time	None	running off a ledge starts a fall, and a fall jumps only just after an unmorph

Every claim about this game, by concept (18)

general	alex-west's M2RoS disassembly of Metroid II, assembled with rgbds, equals Metroid II - Return of Samus (World) byte for byte.	Code
Air control	In a plain jump, `poseFunc_jump` moves Samus 1 px each frame toward a held direction, and not at all when neither is held.	Code
Ammunition	A missile tank adds 10 to Samus's missile capacity and 10 to her missiles, each capped at 999.	Code
Coyote time	Running off a ledge puts Samus straight into the falling pose, and in that pose a jump press starts a jump only while `samus_unmorphJumpTimer` runs, the 16-frame window after she unmorphs in the air.	Code
Health upgrade	A new game starts with 99 units of energy, no energy tanks, and 30 of 30 missiles.	Code
Health upgrade	An energy tank adds a tank, up to 5, and fills Samus's energy, setting its high byte to the tank count and its low byte to 99.	Code
Hitbox	Against the background, Samus is tested at points, one x for the side she moves toward and a list of up to five y offsets for her pose. Against enemies, `collision_samusEnemies` runs first and compares each enemy's hitbox with Samus's, whose top is set per pose.	Code
Invincibility frames	An enemy hit sets `samusInvulnerableTimer` to `$33` (51), and while it is above 0 the hit code returns before any damage. `drawSamus` takes 1 from it each time it draws her, once per frame of play, and blinks her 4 frames on, 4 off.	Code
Jump	Past the held ascent, a jump follows a table: each frame `poseFunc_jump` moves Samus by the next entry of `jumpArcTable`, a signed whole number of pixels from 2 up to 3 down, and the `$80` that ends the table starts a fall.	Code
Knockback	A hit sends Samus away from the side of the enemy she touched along a fixed arc from `.bombArcTable`, 3 px a frame up at first, and 1 px a frame sideways. She can't change direction until the arc's counter reaches `$56`, which the comment calls the end of the rising portion.	Code
Knockback	During knockback a jump press clears `samusInvulnerableTimer` and starts a jump in the air with a ground jump's counter, `$31` or `$21`.	Code
Morph ball	The morph ball needs no item: a Down press while crouching calls `samus_morphOnGround`, and the item bits list bombs, Hi-Jump, Screw Attack, Space Jump, Spring Ball, Spider Ball, and Varia, with no bit for the ball. A new game starts with no item bits set.	Code
Morph ball	In the morph ball, A starts a jump only with the Spring Ball, from a counter of `$2E`.	Code
Running	Walking has no speed variable to build up: `samus_walkRight` adds 1 or 2 px to Samus's X position on alternate frames (1.5 px/frame), 2 px/frame with the Varia Suit, and 1 px/frame in water.	Code
Screw Attack	With the Screw Attack, an enemy Samus touches in a spin jump or its start pose takes a Screw Attack weapon hit, and the contact doesn't hurt her. Solid enemies, whose damage entry is `$FF`, are exempt.	Code
Space Jump	In a spin jump with the Space Jump, a new A press restarts the jump only on frames whose `spaceJumpTable` entry is nonzero: entries 44 to 63, where `jumpArcTable` falls 1 to 3 px a frame. The restart sets the counter to `$28`, or `$18` with the Hi-Jump Boots, below `$40`, so a held A gives a new linear ascent.	Code
Status bar split	The HUD is the window layer, set to X 7. The main game mode's handler sets window Y to `$88` (line 136, the bottom 8 lines), or `$80` (16 lines) to show a message while Samus touches a save point or collects a major item. In the Queen's room the HUD moves to the background layer, because her head uses the window.	Code
Variable jump height	A jump sets `samus_jumpArcCounter` to `$31`, or `$21` with the Hi-Jump Boots. While A is held and the counter is below `$40`, `poseFunc_jump` lifts Samus 2 px each frame, 3 with the boots, and adds 1 to the counter: up to 15 frames, or 31. Letting go sets the counter to `$56`, which the comment calls the start of the arc's falling portion. Before this, `poseFunc_jumpStart` lifts her 2 to 3 px a frame for up to 6 frames while A is held.	Code

References

^alex-west's M2RoS disassembly of Metroid II, assembled with rgbds, equals Metroid II - Return of Samus (World) byte for byte.Code“Metroid II - Return of Samus (World)” · alex-west/M2RoS
How we know
In the cartridge (“Metroid II - Return of Samus (World)”): bank 0 $184A, jumpArcTable, the bytes the jump claims below read. We don't reproduce the bytes.
```
13The resultant file should have this hash: `md5: 9639948ad274fa15281f549e5f9c4d87`
```
readme.md line 13 at 031aea3 · upstream ↗
Checked against the evidence by its author, an AI model, 2026-10-21.
Checked by a second AI model, 2026-10-21.
In the claim ledger

^A jump sets samus_jumpArcCounter to $31, or $21 with the Hi-Jump Boots. While A is held and the counter is below $40, poseFunc_jump lifts Samus 2 px each frame, 3 with the boots, and adds 1 to the counter: up to 15 frames, or 31. Letting go sets the counter to $56, which the comment calls the start of the arc's falling portion. Before this, poseFunc_jumpStart lifts her 2 to 3 px a frame for up to 6 frames while A is held.Codealex-west/M2RoS

How we know

3328        ; High jump parameters
3329        ld a, samus_jumpArrayBaseOffset - $1F ;$21
3330        ld [samus_jumpArcCounter], a
⋮
3337            ; Normal jump parameters
3338            ld a, samus_jumpArrayBaseOffset - $0F ;$31
3339            ld [samus_jumpArcCounter], a

SRC/bank_000.asm lines 3328–3339 at 031aea3 · upstream ↗

3884    ; Check if in linear portion of ascent
3885    ld a, [samus_jumpArcCounter]
3886    cp samus_jumpArrayBaseOffset
⋮
3892            ; Set speed, subtracting an extra 1 from it if we have high jump
⋮
3901        ; If A is not pressed, start falling portion of arc
3902        ld a, samus_jumpArrayBaseOffset + $16 ;56
3903        ld [samus_jumpArcCounter], a

SRC/bank_000.asm lines 3884–3903 at 031aea3 · upstream ↗

3937    ; Increment jump counter
3938    ld a, [samus_jumpArcCounter]
3939    inc a
3940    ld [samus_jumpArcCounter], a

SRC/bank_000.asm lines 3937–3940 at 031aea3 · upstream ↗

4206poseFunc_jumpStart: ;{ 00:19E2 - $09 and $0A - Starting to jump
4207    ; Check if A is pressed
⋮
4211        ; Move up 2 pixel/frame, with an extra pixel 2 out of 4 frames
⋮
4224        ; Increment jump-start counter
⋮
4228        ; Branch ahead if counter has expired
4229        cp $06

SRC/bank_000.asm lines 4206–4229 at 031aea3 · upstream ↗

26def samus_jumpArrayBaseOffset = $40

SRC/constants.asm line 26 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^Past the held ascent, a jump follows a table: each frame poseFunc_jump moves Samus by the next entry of jumpArcTable, a signed whole number of pixels from 2 up to 3 down, and the $80 that ends the table starts a fall.Codealex-west/M2RoS

How we know

3906    ; Get vertical speed from jumpArcTable
3907    sub samus_jumpArrayBaseOffset
3908    ld hl, jumpArcTable
⋮
3913    ; Start falling pose if at the end of the table
3914    cp samus_jumpArrayBaseOffset + $40 ;$80
3915        jr z, .startFalling

SRC/bank_000.asm lines 3906–3915 at 031aea3 · upstream ↗

3927.moveVertical:
3928    call samus_moveVertical

SRC/bank_000.asm lines 3927–3928 at 031aea3 · upstream ↗

4857samus_moveVertical: ;{ 00:1D4E - move down
4858    ; Move up if negative
4859    bit 7, a
4860        jr nz, .moveUp

SRC/bank_000.asm lines 4857–4860 at 031aea3 · upstream ↗

3991; Jump arc table
3992; - This starts being referenced when the jump counter is $40
⋮
3994jumpArcTable: ;{ 00:184A - Jump arc table
3995    db $fe, $fe, $fe, $fe, $ff, $fe, $ff, $fe, $ff, $ff, $ff, $ff, $ff, $ff, $00, $ff
⋮
3999    db $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $80

SRC/bank_000.asm lines 3991–3999 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^Walking has no speed variable to build up: samus_walkRight adds 1 or 2 px to Samus's X position on alternate frames (1.5 px/frame), 2 px/frame with the Varia Suit, and 1 px/frame in water.Codealex-west/M2RoS

How we know

4596    ld b, $01
4597    ; Check if touching water
⋮
4605            ; Varia walking speed
4606            ld b, $02
⋮
4609            ; Normal walking speed (1.5 px/f)
4610            ldh a, [frameCounter]
4611            and $01
4612            add $01
4613            ld b, a
⋮
4616    ; Move Samus right
4617    ldh a, [hSamusXPixel]
4618    add b

SRC/bank_000.asm lines 4596–4618 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^ a bAn enemy hit sets samusInvulnerableTimer to $33 (51), and while it is above 0 the hit code returns before any damage. drawSamus takes 1 from it each time it draws her, once per frame of play, and blinks her 4 frames on, 4 off.Codealex-west/M2RoS

How we know

7802    ; Exit if i-frames are active
7803    ld a, [samusInvulnerableTimer]
7804    and a
7805        ret nz
⋮
7810    ; Give Samus i-frames
7811    ld a, $33
7812    ld [samusInvulnerableTimer], a

SRC/bank_000.asm lines 7802–7812 at 031aea3 · upstream ↗

560drawSamus: ;{ 01:4BD9 Draw Samus
⋮
562    ; Check if damage frames are active
563    ld a, [samusInvulnerableTimer]
564    and a
565    jr z, .endIf_A
566        dec a
567        ld [samusInvulnerableTimer], a
568        ; 4 frames on, 4 frames off

SRC/bank_001.asm lines 560–568 at 031aea3 · upstream ↗

740    call drawSamus_longJump ; Draw Samus

SRC/bank_000.asm line 740 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^A hit sends Samus away from the side of the enemy she touched along a fixed arc from .bombArcTable, 3 px a frame up at first, and 1 px a frame sideways. She can't change direction until the arc's counter reaches $56, which the comment calls the end of the rising portion.Codealex-west/M2RoS

How we know

7824    ; Set travel direction to damage boost direction
7825    ld a, [samus_damageBoostDirection]
7826    ld [samusAirDirection], a
⋮
7832        ld [samusAirDirection], a
⋮
7835    ; Set jump arc counter to base
7836    ld a, samus_jumpArrayBaseOffset

SRC/bank_000.asm lines 7824–7836 at 031aea3 · upstream ↗

8840    ; If Samus was on the left side of the enemy
⋮
8845        ; If so, change the damage boost value to the left
8846        ld a, $ff
8847        ld [samus_damageBoostDirection], a

SRC/bank_000.asm lines 8840–8847 at 031aea3 · upstream ↗

2439poseFunc_bombed: ;{ 00:0F6C - $11: Bombed (standing)
2440    ; Load y speed from bombArcTable

SRC/bank_000.asm lines 2439–2442 at 031aea3 · upstream ↗

2469    ; Don't let Samus change aerial direction during the rising portion of the knockback
2470    cp samus_jumpArrayBaseOffset + $16 ; $56

SRC/bank_000.asm lines 2469–2470 at 031aea3 · upstream ↗

2525.bombArcTable: ; 00:0FF6
2526    db $fd, $fd, $fd, $fd, $fe, $fd, $fe, $fd, $fe, $fe, $fe, $fe, $fe, $fe, $ff, $fe

SRC/bank_000.asm lines 2525–2529 at 031aea3 · upstream ↗

2491    ; Move right if applicable
2492    ld a, [samusAirDirection]
2493    cp $01
2494    jr nz, .endIf_F
2495        call samus_moveRightInAir.noTurn

SRC/bank_000.asm lines 2491–2495 at 031aea3 · upstream ↗

4785.noTurn: ; 00:1CFA Alternate entry
4786    ; Set speed
4787    ld a, $01
4788    ld b, a

SRC/bank_000.asm lines 4785–4788 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^During knockback a jump press clears samusInvulnerableTimer and starts a jump in the air with a ground jump's counter, $31 or $21.Codealex-west/M2RoS

How we know

2350poseFunc_hurt: ;{ 00:0EF7 - $0F - Knockback
2351    ; Go to "bombed" pose handler if jump is not pressed
⋮
2355    ; Do a mid-air jump
⋮
2361    ; Clear i-frames
2362    xor a
2363    ld [samusInvulnerableTimer], a
⋮
2366    ld a, samus_jumpArrayBaseOffset - $1F ;$21
⋮
2375        ld a, samus_jumpArrayBaseOffset - $0F ;$31

SRC/bank_000.asm lines 2350–2376 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^The morph ball needs no item: a Down press while crouching calls samus_morphOnGround, and the item bits list bombs, Hi-Jump, Screw Attack, Space Jump, Spring Ball, Spider Ball, and Varia, with no bit for the ball. A new game starts with no item bits set.Codealex-west/M2RoS
How we know
```
3705; Handle down input
3706    ; Rising edge
3707    ldh a, [hInputRisingEdge]
3708    bit PADB_DOWN, a
3709    jr z, .endIf_L
3710        call samus_morphOnGround
```
SRC/bank_000.asm lines 3705–3710 at 031aea3 · upstream ↗
```
4524samus_morphOnGround: ;{ 00:1BA4
4525    ; Set pose
4526    ld a, pose_morph
4527    ld [samusPose], a
```
SRC/bank_000.asm lines 4524–4527 at 031aea3 · upstream ↗
```
49def itemMask_bomb   = %00000001 ; 01: Bombs
⋮
53def itemMask_spring = %00010000 ; 10: Spring ball
54def itemMask_spider = %00100000 ; 20: Spider ball
55def itemMask_varia  = %01000000 ; 40: Varia suit
56def itemMask_UNUSED = %10000000 ; 80: Unused
```
SRC/constants.asm lines 49–56 at 031aea3 · upstream ↗
```
20    db $00       ; Samus' equipment
```
SRC/data/initialSave.asm line 20 at 031aea3 · upstream ↗
Checked against the evidence by its author, an AI model, 2026-10-21.
Checked by a second AI model, 2026-10-21.
In the claim ledger

^In the morph ball, A starts a jump only with the Spring Ball, from a counter of $2E.Codealex-west/M2RoS

How we know

3780    ; Handle spring ball
3781    ; Check if A is pressed
3782    ldh a, [hInputPressed]
3783    bit PADB_A, a
3784    jr z, .endIf_C
3785        ; Check if we have spring ball
3786        ld a, [samusItems]
3787        bit itemBit_spring, a
3788        jr z, .endIf_C
3789            ; Set jump parameter
3790            ld a, samus_jumpArrayBaseOffset - $12 ;$2e

SRC/bank_000.asm lines 3780–3793 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

^In a spin jump with the Space Jump, a new A press restarts the jump only on frames whose spaceJumpTable entry is nonzero: entries 44 to 63, where jumpArcTable falls 1 to 3 px a frame. The restart sets the counter to $28, or $18 with the Hi-Jump Boots, below $40, so a held A gives a new linear ascent.Codealex-west/M2RoS

How we know

4002; Space Jump Table
4003; - $00 means no space jumping on that frame
4004; - Non-zero values mean that you can space jump on that frame
⋮
4006spaceJumpTable: ;{ 00:1899
⋮
4009    db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $02, $01, $02, $02
4010    db $02, $02, $03, $02, $02, $03, $02, $02, $03, $02, $03, $02, $03, $02, $03, $02
4011    db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $80

SRC/bank_000.asm lines 4002–4011 at 031aea3 · upstream ↗

3997    db $00, $01, $01, $00, $01, $01, $01, $01, $01, $01, $02, $01, $02, $01, $02, $02
3998    db $02, $02, $03, $02, $02, $03, $02, $02, $03, $02, $03, $02, $03, $02, $03, $02

SRC/bank_000.asm lines 3997–3998 at 031aea3 · upstream ↗

4014poseFunc_spinJump: ;{ 00:18E8 - $02: Spin jumping
⋮
4016    ldh a, [hInputRisingEdge]
⋮
4023    ; If jump timer is > $40, then jump ahead
4024    ld a, [samus_jumpArcCounter]
4025    cp samus_jumpArrayBaseOffset
4026    jr nc, .endIf_B
4027        ; Handle linear ascent of the jump
⋮
4030        bit PADB_A, a
⋮
4034            ld a, [samusItems]
⋮
4053    ; Skip ahead if not holding jump
4054    ldh a, [hInputRisingEdge]
4055    bit PADB_A, a
⋮

SRC/bank_000.asm lines 4014–4078 at 031aea3 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-21.

Checked by a second AI model, 2026-10-21.

In the claim ledger

Sources

Code

1991. “Metroid II - Return of Samus (World).” · licence, all uses
alex-west. 2026. “M2RoS: Return of Samus Disassembly.” Commit 031aea3. alex-west/M2RoS @ 031aea3 · licence, all uses

Related

See also

Mentioned in

Mechanics

References

Sources

Code