nes-contra-us/docs/Game Completion Modifier.md

Overview

Contra is already a challenging game. However, it gets even more difficult the more times you beat the game. This documents the ways in which beating the game affects the behavior of subsequent playthoughs.

The game keeps track of the number of times the player(s) beat the game in the variable GAME_COMPLETION_COUNT, located at CPU memory address $31.

Many of the HP modifications are also based on the player's "weapon strength". This variable, called PLAYER_WEAPON_STRENGTH, is stored at CPU memory address $2f and depends on which weapon player 1 has.

Weapon	Strength
Default	0
M	2
F	1
S	3
L	2

Soldier Generation

Random soldiers are generated more quickly the more you beat the game up until you've beaten the game 3 times. The actual delay depends on the level. Each time you beat the game, the delay is lowered by 40 (assuming the weapon player 1 has is the same).

Soldier generation delay is calculated by the following formula

DELAY = INITIAL_LEVEL_DELAY - (40 * GAME_COMPLETION_COUNT) - (5 * PLAYER_WEAPON_STRENGTH)

Completion Count	Result (hex)	Result (decimal)
0	#$81	129
1	#$59	89
2	#$31	49
3	#$09	9
4	#$09	9

All sample results assume the player's PLAYER_WEAPON_STRENGTH is 3 (S weapon) and the level is 1 where the initial delay is 144. The initial level delays are as follows (defined in level_soldier_generation_timer)

Level	Delay (decimal)
1	144
2	n/a
3	216
4	n/a
5	208
6	200
7	192
8	n/a

Red Turret Attack Delay

Red turret attack delay is shorter if you've beaten the game once. It doesn't get any short for subsequent wins.

Completion Count	Result (hex)	Result (decimal)
0	#$28	40
1	#$08	8

Alien Fetus (Bundle) HP

The level 8 alien fetus (bundle) HP goes up as you beat the game more and more. It is the number of times you've beaten the game + 2, so the HP goes up by 1 every time the game is beaten (until max 255 due to memory limit).

GAME_COMPLETION_COUNT + 2

Completion Count	Result (hex)	Result (decimal)
0	#$02	2
1	#$03	3
2	#$04	4
3	#$05	5
4	#$06	6
5	#$07	7
...	...	...
253	#$ff	255
254	#$00	0 (invincible)
255	#$01	1

Alien Mouth (Wadder) HP

The level 8 alien mouth (wadder) HP goes up as you beat the game more and more. The HP is calculated by the following formula

(2 * GAME_COMPLETION_COUNT) + PLAYER_WEAPON_STRENGTH + 4

Completion Count	Result (hex)	Result (decimal)
0	#$07	7
1	#$09	9
2	#$0b	11
3	#$0d	13
4	#$0f	15
5	#$11	17
...	...	...
124	#$ff	255
125	#$01	1
...	...	...
252	#$00	0 (invincible)

All sample results assume the player's PLAYER_WEAPON_STRENGTH is 3 (S weapon).

Alien Spider (Bugger) HP

Level 8 alien spiders (buggers) HP goes up as you beat the game more and more. The HP is calculated by the following formula

PLAYER_WEAPON_STRENGTH + GAME_COMPLETION_COUNT + 2

Completion Count	Result (hex)	Result (decimal)
0	#$05	5
1	#$06	6
2	#$07	7
3	#$08	8
4	#$09	9
5	#$0a	11
...	...	...
250	#$ff	255
251	#$00	0 (invincible)
252	#$02	2

All sample results assume the player's PLAYER_WEAPON_STRENGTH is 3 (S weapon).

Alien Spider Spawn (Eggron) HP

(GAME_COMPLETION_COUNT * 2) + (PLAYER_WEAPON_STRENGTH * 2) + 24

Completion Count	Result (hex)	Result (decimal)
0	#$1e	30
1	#$20	32
2	#$22	34
3	#$24	36
4	#$26	38
5	#$28	40
...	...	...
112	#$fe
113	#$00	0 (invincible)
114	#$02	2

All sample results assume the player's PLAYER_WEAPON_STRENGTH is 3 (S weapon).

Alien Guardian & Boss Heart HP

The level 8 alien guardian and boss heart (final boss) HP are both calculated according to the same formula below until the calculated HP is greater than or equal to #$a0 (160 decimal). 160 is the max HP the alien guardian and boss heart can be.

(PLAYER_WEAPON_STRENGTH * 16) + 55 + (GAME_COMPLETION_COUNT * 16)

Completion Count	Result (hex)	Result (decimal)
0	#$67	103
1	#$77	119
2	#$87	135
3	#$97	151
4	#$a0	160
5	#$a0	160

All sample results assume the player's PLAYER_WEAPON_STRENGTH is 3 (S weapon).