Mechanic · time & pacing · fixed shooter, maze, platformer

Difficulty ramp

Rules that make later levels, or longer play within a level, harder.

stubAlso: difficulty curve, level difficulty, progressive difficultyUpdated 2026-10-21
On this page
  1. Related
  2. Games
  3. References
  4. Sources

A difficulty ramp makes later play harder by rule. Space Invaders starts each new rack lower1. Pac-Man steps through a table of per-level settings2. Galaxian and Donkey Kong add a part that rises with time spent in the level to one that rises per level3,4. Asteroids starts each wave with more large rocks, up to a cap: 4, 6, 8, 10, then 11 rocks5. Defender reads each wave’s enemy counts from a table, as Pac-Man reads its levels, and repeats the fourth wave’s counts after that6,2.

  • Start positionSpace Invaders (1978). Each new rack starts lower, from an 8-entry table.1
  • More enemiesAsteroids (1979). Each wave starts two more large rocks, up to 11.5
  • Level tablePac-Man (1980). Each level advances one entry along a DIP-selected table until it reads 20.2Defender (1981). Enemy counts for waves 1 to 4 from a table, the fourth repeated after.6
  • Level and timeGalaxian (1979). A base that rises per level plus an extra part that rises with time in the level.3Donkey Kong (1981). The level number plus a timer on the board, capped at 5; the bonus timer grows with the level.4,7

See also

Mentioned in

Lineage

Games

GameYearHowNote
Factorio2016the enemy grows stronger with play time and with the pollution the factory makes
Space Invaders1978Start positioneach new rack starts lower, from an 8-entry table
Asteroids1979More enemieseach wave starts two more large rocks, up to 11
Pac-Man1980Level tableeach level advances one entry along a DIP-selected table until it reads 20
Defender1981Level tableenemy counts for waves 1 to 4 from a table, the fourth repeated after
Galaxian1979Level and timea base that rises per level plus an extra part that rises with time in the level
Donkey Kong1981Level and timethe level number plus a timer on the board, capped at 5; the bonus timer grows with the level
Super Mario Bros.: The Lost Levels1986Level flagfrom 4-4 on, and in worlds A to D, extra enemies appear and hammer bros, Bowser, and the cannons get more aggressive
Every claim about this mechanic, by game (10)
Space Invaders 1978Each new rack starts lower on the screen. The first rack's bottom row starts at Y $78. When a rack is cleared, the count of racks beaten (taken mod 8, plus 1) picks the next start from an 8-entry table, $60, $50, $48, $48, $48, $40, $40, $40, so the 10th rack starts where the 2nd did.Code
Asteroids 1979A new wave starts once no rocks are left and a 127-frame wave timer, set when the last rock goes, has run out. Each wave has two more large rocks than the one before, up to 11; the count starts at 2 when a game starts, so the waves run 4, 6, 8, 10, 11, 11 (computed).Code
Galaxian 1979Galaxian's difficulty has two parts. A base value rises by 1 with each level cleared, up to 7. An extra value starts each level at 0 and rises by 1 each time two nested counters run out, up to 7. The counters reload to 60 and 20, so once running they step it every 1,200 passes of the game logic, but the cited code doesn't reset them when a level starts, so a level's first step can come sooner. They hold while the player is not in play or after a flagship in flight is shot. The two values set how many single attackers may fly at once and how many attack counters tick.Code
Pac-Man 1980Each new level advances a pointer one entry along a difficulty table until the entry reads $14 (20). The DIP switch picks the table: one runs 0, 1, 2, … 20 and reaches 20 on level 21; the other, which the comment calls hard, runs 1, 3, 4, 6, 7, 8, … 17, 20 and reaches 20 on level 16. Each entry selects a 6-byte record at $0796 that sets, among other things, the movement pattern and the ghosts' counters for leaving the house.Code
Defender 1981Defender reads each wave's enemies from a table with a column for each of waves 1 to 4: landers 15, 20, 20, 20; bombers 0, 3, 4, 5; pods 0, 1, 3, 4; no mutants or swarmers at the start; landers come in groups of 5. Later waves take the fourth column plus per-wave increments, which are 0 for these counts, so they keep the fourth wave's numbers (computed).Code
Donkey Kong 1981Each board's bonus timer starts at 10 × level + 40, computed in 8 bits and capped at 80, and the readout shows 100 times the value: 5,000 on level 1, 6,000 on level 2, 7,000 on level 3, and 8,000 from level 4. The listings read MAME's dkong set (US set 1).Code
Donkey Kong's internal difficulty, which the comments say sets the speed of fires and the behavior of wild barrels, is the level number plus a timer that steps once every 2,048 calls of its routine (256 × 8), capped at 5.Code
Super Mario Bros.: The Lost Levels 1986Every area from World 4-4 on, and every area of worlds A to D, starts with the secondary hard mode flag set; the areas of worlds 1 to 3 and 4-1 to 4-3 start without it. The memory clear at the start of each area resets it first.Code
With the secondary hard mode flag set: enemies the level data marks for hard mode appear, where otherwise they are skipped; a Bullet Bill cannon is picked to fire when a pseudorandom number masked to three bits is below 6 (6 of 8 values, against 6 of 16 with four bits); up to four flying Cheep Cheeps at once instead of three; hammer bros throw on a shorter timer ($1C against $30), can take the longer of two jump timers ($37 against $20), and in worlds 1 to 6 wait a shorter time before walking left ($50 against $80; in worlds 7 to 9 they don't wait either way, and worlds A to D, which share world numbers 1 to 4 and always have the flag, take $50); Bloopers pick a new direction when two pseudorandom bits are clear rather than six, and then a Blooper in an even enemy slot turns toward the player, one in an odd slot takes the player's moving direction; Bowser's fire breath and the flames that fly in on their own come 16 timer ticks sooner, and the flames move faster ($60 subtracted from their fractional position each frame, against $40); and the large lifts are drawn four sprites wide instead of six with a smaller box, as they always are in castles, with balance platforms and their ropes placed for the shorter width.Code
The code keeps the primary hard mode flag's checks, which turn Goombas into Buzzy Beetles, start walking enemies faster ($F4 against $F8), and revive stomped enemies sooner and send them off faster. Nothing in The Lost Levels' code sets the flag, and starting a game clears it, so none of these takes effect. Super Mario Bros. sets it from its world select flag when a game starts.Code

References

  1. ^ abEach new rack starts lower on the screen. The first rack's bottom row starts at Y $78. When a rack is cleared, the count of racks beaten (taken mod 8, plus 1) picks the next start from an 8-entry table, $60, $50, $48, $48, $48, $40, $40, $40, so the 10th rack starts where the 2nd did.CodeComputer Archeology, Space Invadersrevised
    How we know
    17170A09: 2E FE           LD      L,$FE               ; 2xFE ... rack count
17180A0B: 7E              LD      A,(HL)              ; Get the number of racks the player has beaten
17190A0C: E6 07           AND     $07                 ; 0-7
17200A0E: 3C              INC     A                   ; Now 1-8
17210A0F: 77              LD      (HL),A              ; Update count since player just beat a rack
17220A10: 21 A2 1D        LD      HL,$1DA2            ; Starting coordinate of alien table
17230A13: 23              INC     HL                  ; Find the ...
17240A14: 3D              DEC     A                   ; ... right entry ...
17250A15: C2 13 0A        JP      NZ,$0A13            ; {} ... in the table
17260A18: 7E              LD      A,(HL)              ; Get the starting Y coordiante
17270A19: E1              POP     HL                  ; Restore player's pointer
17280A1A: 2E FC           LD      L,$FC               ; 2xFC ...
⋮
    content/Arcade/SpaceInvaders/Code.md lines 1717–1731 at 1adc2a7 · upstream ↗
    4685AlienStartTable:
4686; Starting Y coordinates for aliens at beginning of rounds. The first round is initialized to $78 at 07EA.
4687; After that this table is used for 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, and 9th. The 10th starts over at
4688; 1DA3 (60).
46891DA3: 60                                    
46901DA4: 50                                    
46911DA5: 48                                    
46921DA6: 48                                    
46931DA7: 48                                    
46941DA8: 40                                    
46951DA9: 40                                    
46961DAA: 40
    content/Arcade/SpaceInvaders/Code.md lines 4685–4696 at 1adc2a7 · upstream ↗
    137807EA: 21 78 38        LD      HL,$3878            ; Screen coordinates for lower-left alien
137907ED: 22 FC 21        LD      ($21FC),HL          ; {ram.p1RefAlienY} Initialize reference alien for player 1
    content/Arcade/SpaceInvaders/Code.md lines 1378–1379 at 1adc2a7 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-25.

    Revised after a check by a second AI model, 2026-10-21.

    Checked by a second AI model, 2026-10-25.

    In the claim ledger

  2. ^ abcEach new level advances a pointer one entry along a difficulty table until the entry reads $14 (20). The DIP switch picks the table: one runs 0, 1, 2, … 20 and reaches 20 on level 21; the other, which the comment calls hard, runs 1, 3, 4, 6, 7, 8, … 17, 20 and reaches 20 on level 16. Each entry selects a 6-byte record at $0796 that sets, among other things, the movement pattern and the ghosts' counters for leaving the house.Codemburkley/pacman-crevised
    How we know
    273    /*  Difficulty data.  Two sets, easy or hard.  Hard ramps up more quickly.
274     *  Each level is more difficult until max difficulty which is 0x14 */
⋮
277    // 0068                           00 01 02 03 04 05 06 07
278    // 0070  08 09 0a 0b 0c 0d 0e 0f  10 11 12 13 14 
⋮
281    // 007d                                          01 03 04
282    // 0080  06 07 08 09 0a 0b 0c 0d  0e 0f 10 11 14
    pacman.c lines 273–282 at 3277e56 · upstream ↗
    11406    DIFFICULTY_PTR = DIFFICULTY_DATA[DIP_SWITCH_DIFFICULTY ^ 1];
    pacman.c line 11406 at 3277e56 · upstream ↗
    3164    if (ROM[P1_CURR_DIFFICULTY] == 0x14)
3165        return;
⋮
3172    P1_CURR_DIFFICULTY++;
    pacman.c lines 3153–3172 at 3277e56 · upstream ↗
    2221void setupGhostTimers_070e (int b)
⋮
2232        b = ROM[P1_CURR_DIFFICULTY];
⋮
2247    uint8_t *ix = DATA_0796 + b * 6;
⋮
2270    setupMovePat_0814(hl);
⋮
2292    initLeaveHouseCounters_083a(hl);
    pacman.c lines 2221–2292 at 3277e56 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-25.

    Revised after a check by a second AI model, 2026-10-21.

    Checked by a second AI model, 2026-10-25.

    In the claim ledger

  3. ^ abGalaxian's difficulty has two parts. A base value rises by 1 with each level cleared, up to 7. An extra value starts each level at 0 and rises by 1 each time two nested counters run out, up to 7. The counters reload to 60 and 20, so once running they step it every 1,200 passes of the game logic, but the cited code doesn't reset them when a level starts, so a level's first step can come sooner. They hold while the player is not in play or after a flagship in flight is shot. The two values set how many single attackers may fly at once and how many attack counters tick.CodeScottTunstall/Galaxianrevised
    How we know
    493; These 2 counters are used to gradually increase the DIFFICULTY_EXTRA_VALUE over time. See $14F3 for algorithm details.
⋮
497; These values determine how often aliens attack (see $1524 and $1583), and how many can attack at one time (see $1352). 
498DIFFICULTY_EXTRA_VALUE              EQU $421A         ; DIFFICULTY_EXTRA_VALUE is incremented during the level. Maximum value of 7. See $1509.  
499DIFFICULTY_BASE_VALUE               EQU $421B         ; DIFFICULTY_BASE_VALUE is incremented when you complete a level. Maximum value of 7. See $1656.
    galaxian.asm lines 493–499 at a16b402 · upstream ↗
    5183HANDLE_LEVEL_DIFFICULTY:
518414F3: 3A 00 42      ld   a,($4200)           ; read HAS_PLAYER_SPAWNED
518514F6: 0F            rrca                     ; move flag into carry
518614F7: D0            ret  nc                  ; return if player has not spawned
518714F8: 3A 2B 42      ld   a,($422B)           ; read IS_FLAGSHIP_HIT
518814FB: 0F            rrca                     ; move flag into carry
518914FC: D8            ret  c                   ; return if flagship has been hit
⋮
519214FD: 21 18 42      ld   hl,$4218            ; load HL with address of DIFFICULTY_COUNTER_1
51931500: 35            dec  (hl)                ; decrement counter
51941501: C0            ret  nz
51951502: 36 3C         ld   (hl),$3C            ; reset counter
⋮
51981504: 23            inc  hl                  ; bump HL to DIFFICULTY_COUNTER_2
⋮
    galaxian.asm lines 5183–5214 at a16b402 · upstream ↗
    55041649: AF            xor  a
5505164A: 32 1A 42      ld   ($421A),a           ; reset DIFFICULTY_EXTRA_VALUE
⋮
55111656: 2A 1B 42      ld   hl,($421B)          ; load H with PLAYER_LEVEL and L with DIFFICULTY_BASE_VALUE
55121659: 24            inc  h                   ; increment player level 
5513165A: 7D            ld   a,l                 ; load A with DIFFICULTY_BASE_VALUE
5514165B: FE 07         cp   $07                 ; are we at max difficulty?
5515165D: 28 03         jr   z,$1662             ; yes, goto $1662
⋮
55171661: 3C            inc  a                   ; otherwise, increment DIFFICULTY_BASE_VALUE
55181662: 6F            ld   l,a
55191663: 22 1B 42      ld   ($421B),hl          ; update PLAYER_LEVEL and DIFFICULTY_BASE_VALUE
    galaxian.asm lines 5504–5519 at a16b402 · upstream ↗
    2040HANDLE_MAIN_GAME_LOGIC:
    galaxian.asm lines 2040–2055 at a16b402 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-25.

    Revised after a check by a second AI model, 2026-10-21.

    Checked by a second AI model, 2026-10-25.

    In the claim ledger

  4. ^ abDonkey Kong's internal difficulty, which the comments say sets the speed of fires and the behavior of wild barrels, is the level number plus a timer that steps once every 2,048 calls of its routine (256 × 8), capped at 5.Codefurrykef/dkdasmrevised
    How we know
    439; #6380 - Internal difficulty. Dictates speed of fires, wild barrel behavior, barrel steerability and other things. Ranges from 1 to 5.
    dkong.asm line 439 at 4d296c5 · upstream ↗
    1633; checks timers and increments difficulty if needed
⋮
1635; [timer_6384++ ; IF timer_6384 != 256 THEN RETURN ; timer_6384 := 0 ; ]
⋮
1643; [timer_6381++ ; IF (timer_6381/8) != INT(timer_6381/8) THEN RETURN]
⋮
1654; [ difficulty := (timer_6381 div 8) + level ; IF difficulty > 5 THEN difficulty := 5 ; RETURN]
    dkong.asm lines 1633–1669 at 4d296c5 · upstream ↗

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

    Revised after a check by a second AI model, 2026-10-21.

    In the claim ledger

  5. ^ abA new wave starts once no rocks are left and a 127-frame wave timer, set when the last rock goes, has run out. Each wave has two more large rocks than the one before, up to 11; the count starts at 2 when a game starts, so the waves run 4, 6, 8, 10, 11, 11 (computed).CodeComputer Archeology, Asteroids
    How we know
    JSR $6EFA ; {} Reset Sound, Zero Out Sound Timers JSR $6ED8 ; {} Number Of Starting Ships To $56 And Zero JSR $7168 ; {} Start of main game loop???
    content/Arcade/Asteroids/Code.md#L29-L31 · upstream ↗
    JSR $6885 ; {} BCS $6803 ; {}
    content/Arcade/Asteroids/Code.md#L54-L55 · upstream ↗
    ASL A ; Zero A, And Set Carry Flag
    content/Arcade/Asteroids/Code.md#L150-L152 · upstream ↗
    LDA #$02 STA $02F5 ; {ram.asteroidsPerWave}
    content/Arcade/Asteroids/Code.md#L858-L859 · upstream ↗
    LDA $02FB ; {ram.astdWaveTimer} BEQ $687E ; {} DEC $02FB ; {ram.astdWaveTimer} ORA $02F6 ; {ram.curAsteroidCount} BNE $680C ; {} BEQ $6809 ; {}
    content/Arcade/Asteroids/Code.md#L76-L81 · upstream ↗
    DEC $02F6 ; {ram.curAsteroidCount} BNE $6F8C ; {} LDY #$7F STY $02FB ; {ram.astdWaveTimer}
    content/Arcade/Asteroids/Code.md#L939-L942 · upstream ↗
    LDA $02F5 ; {ram.asteroidsPerWave} CLC ADC #$02 CMP #$0B BCC $7193 ; {} Branch if smaller??? LDA #$0B STA $02F6 ; {ram.curAsteroidCount} STA $02F5 ; {ram.asteroidsPerWave} … AND #$18 ORA #$04 STA $0200,X ; {ram.statusAsteroids}
    content/Arcade/Asteroids/Code.md#L1182-L1197 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-22.

    Checked by a second AI model, 2026-10-22.

    In the claim ledger

  6. ^ abDefender reads each wave's enemies from a table with a column for each of waves 1 to 4: landers 15, 20, 20, 20; bombers 0, 3, 4, 5; pods 0, 1, 3, 4; no mutants or swarmers at the start; landers come in groups of 5. Later waves take the fourth column plus per-wave increments, which are 0 for these counts, so they keep the fourth wave's numbers (computed).Codemwenge/defender
    How we know
    674*WAVE DATA
675*MAX,MIN,INTRADELT,INTERDELT
676*W1,W2,W3,W4
677WVTAB   FCB    20,0,0,0
678        FCB    15,20,20,20      ;LANDERS
679        FCB    3,0,0,0
680        FCB    0,3,4,5          ;TIES
681        FCB    6,0,0,0
682        FCB    0,1,3,4          ;PROBES
683        FCB    10,0,0,0
684        FCB    0,0,0,0          ;SCHITZOS
685        FCB    10,0,0,0
⋮
    src/blk71.src lines 674–690 at e740063 · upstream ↗
    1865        LDA    PWAV,X
1866        PSHS   A
1867        CMPA   #4
1868        BLS    GETWV1
1869        LDA    #4
1870GETWV1  LDU    WVTAB
1871        ADDA   #3               ;OFFSET ADJUST
⋮
1878GETWV3  PULS   A                ;HIGHER THAN 4?
⋮
1895GETWV4  LDB    #3
⋮
1898        BSR    WDELT            ;GET YUR DELTAS
    src/defa7.src lines 1864–1900 at e740063 · upstream ↗
    1145        FDB    LANDV
1146        FDB    MUTV
1147        FDB    BAITV
1148        FDB    BOMBV
1149        FDB    SWRMPV
1150        FDB    SWARMV
⋮
1161PICTS   FDB    LNDP1
1162        FDB    SCZP1
1163        FDB    UFOP1
1164        FDB    TIEP1
1165        FDB    PRBP1
1166        FDB    SWPIC1
    src/amode1.src lines 1144–1166 at e740063 · upstream ↗
    271SWRMP   FDB    POD
⋮
274BOMBR   FDB    BOMBER
    src/mess0.src lines 271–274 at e740063 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-22.

    Checked by a second AI model, 2026-10-22.

    In the claim ledger

  7. ^Each board's bonus timer starts at 10 × level + 40, computed in 8 bits and capped at 80, and the readout shows 100 times the value: 5,000 on level 1, 6,000 on level 2, 7,000 on level 3, and 8,000 from level 4. The listings read MAME's dkong set (US set 1).Codefurrykef/dkdasm · Computer Archeology, Donkey Kongrevised
    How we know
    3746; set up initial timer
3747; timer is either 5000, 6000, 7000 or 8000 depending on level
    dkong.asm lines 3746–3768 at 4d296c5 · upstream ↗
    7>>> binary 0000:roms/c_5et_g.bin + roms/c_5ct_g.bin + roms/c_5bt_g.bin + roms/c_5at_g.bin
    content/Arcade/DonkeyKong/Code.md line 7 at 1adc2a7 · upstream ↗
    LD A,($6229) ; {hard.workRam+229} the bonus scales with the level … ADD A,$28 ; plus 40; the readout shows 100 times this CP $51 … LD A,$50 ; clamped at 80
    content/Arcade/DonkeyKong/Code.md#L3171-L3184 · upstream ↗

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

    Revised after a check by a second AI model, 2026-10-21.

    In the claim ledger

Sources

Code