Mechanic · enemies & ai · multidirectional shooter

Enemy splitting

An enemy that breaks into smaller enemies when hit, rather than dying outright.

stubAlso: splitting, split on hit, splitting enemiesUpdated 2026-10-22
On this page
  1. Related
  2. Games
  3. References
  4. Sources

An enemy that splits multiplies the targets each shot makes. Each Asteroids rock leaves two of the next size down, until the small ones, which leave nothing1.

  • HalvingAsteroids (1979). Large rocks leave two medium, medium two small, for 20, 50, and 100 points.1

See also

Games

GameYearHowNote
Asteroids1979Halvinglarge rocks leave two medium, medium two small, for 20, 50, and 100 points
Every claim about this mechanic, by game (1)
Asteroids 1979A rock that is hit, by the ship, the saucer, or either's shots, halves its size code (large 4, medium 2, small 1): a large rock leaves two medium rocks, a medium rock two small ones, and a small rock none. Each piece takes its parent's position and velocity, adds a random −16 to +15 to each axis, and holds each axis to a speed of 6 to 31. The first piece's horizontal position and the second's vertical one are changed by XOR with twice the low five bits of that piece's velocity. The hit rock becomes an explosion. A piece needs a free slot of the 27, so a full field gives fewer. During a game, a hit by the ship or its shots scores 20 for a large rock, 50 for a medium one, and 100 for a small one.Code

References

  1. ^ abA rock that is hit, by the ship, the saucer, or either's shots, halves its size code (large 4, medium 2, small 1): a large rock leaves two medium rocks, a medium rock two small ones, and a small rock none. Each piece takes its parent's position and velocity, adds a random −16 to +15 to each axis, and holds each axis to a speed of 6 to 31. The first piece's horizontal position and the second's vertical one are changed by XOR with twice the low five bits of that piece's velocity. The hit rock becomes an explosion. A piece needs a free slot of the 27, so a full field gives fewer. During a game, a hit by the ship or its shots scores 20 for a large rock, 50 for a medium one, and 100 for a small one.CodeComputer Archeology, Asteroids
    How we know
    JSR $75EC ; {} … LDA #$A0 STA $0200,Y ; {ram.statusAsteroids}
    content/Arcade/Asteroids/Code.md#L421-L435 · upstream ↗
    LDA $0200,Y ; {ram.statusAsteroids} AND #$07 LSR A TAX BEQ $7605 ; {} ORA $0E ; {ram.$0E} STA $0200,Y ; {ram.statusAsteroids} LDA $1C ; {ram.numPlayers} Number Of Players In Current Game BEQ $761D ; {} None, Branch LDA $0D ; {ram.$0D} BEQ $7614 ; {} CMP #$04 …
    content/Arcade/Asteroids/Code.md#L1740-L1788 · upstream ↗
    JSR $77B5 ; {} AND #$8F BPL $720C ; {} ORA #$F0 CLC ADC $0223,Y ; {ram.horzVelAsteroids} JSR $7233 ; {} … CMP #$E1 … CMP #$FB … …
    content/Arcade/Asteroids/Code.md#L1236-L1270 · upstream ↗
    LDX #$1A LDA $0200,X ; {ram.statusAsteroids} BEQ $7464 ; {} DEX BPL $745C ; {}
    content/Arcade/Asteroids/Code.md#L1531-L1536 · 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

Sources

Code