Add function to force a mon gender

Add a function to force a mon gender, like for Cubone Mother in the Pokemon Tower.
Only bi-gendered mons can have their gender forced.
Roll a random attack DV that satisfy the mon gender ratio condition.

color/colorplus/mon_gender.asm

@@ -1,4 +1,3 @@
-IF GEN_2_GRAPHICS
 ; Used  to define gender ratios
 	DEF MALE_ONLY         EQU $00
 	DEF MALE_88_PERCENT   EQU $1F
@@ -7,7 +6,6 @@ IF GEN_2_GRAPHICS
 	DEF FEMALE_75_PERCENT EQU $BF
 	DEF FEMALE_ONLY       EQU $FE
 	DEF NO_GENDER         EQU $FF
-ENDC
 
 ; Determine a Pokémon's gender based on its DVs
 ; This uses the same formula as Gen 2, so gender should match if you trade them forward via Time Capsule
@@ -24,6 +22,8 @@ GetMonGender::
 	ld hl, MonGenderRatios
 	add hl, bc ; hl now points to the species gender ratio
 
+	call CheckForcedGender
+
 ; Attack DV
 	ld a, [de]
 	and $f0
@@ -66,6 +66,54 @@ GetMonGender::
 	ld [wPokedexNum], a
 	ret
 
+CheckForcedGender:
+	ld a, [hl]
+	and a ; cp MALE_ONLY
+	ret z
+	cp FEMALE_ONLY
+	ret nc
+
+	push hl
+	ld hl, wGenderFlags
+	bit 0, [hl] ; check if force male
+	res 0, [hl]
+	jr nz, .forceMale
+	bit 1, [hl] ; check if force female
+	res 1, [hl]
+	jr z, .done
+
+	ld hl, .checkFemaleDV
+	jr .forceCommon
+.forceMale
+	ld hl, .checkMaleDV
+.forceCommon
+	and $0F
+	inc a
+	ld b, a
+
+.rerollAttackDV
+	call Random
+	and $0F
+	cp b
+	jp hl
+
+.checkMaleDV
+	jr c, .rerollAttackDV
+	jr .gotAttackDV
+.checkFemaleDV
+	jr nc, .rerollAttackDV
+
+.gotAttackDV
+	ld b, a
+	swap b
+	ld a, [de]
+	and $0F
+	or b
+	ld [de], a
+.done
+	pop hl
+	ret
+
 MonGenderRatios:
 	db MALE_88_PERCENT   ; Bulbasaur
 	db MALE_88_PERCENT   ; Ivysaur

ram/wram.asm

@@ -1894,7 +1894,11 @@ wPlayerCoins:: dw ; BCD
 wMissableObjectFlags:: flag_array $100
 wMissableObjectFlagsEnd::
 
-	ds 2
+	ds 1
+
+;; bit 0 - force male gender
+;; bit 1 - force female gender
+wGenderFlags:: db
 
 wAnimationStatus:: db
 

scripts/PokemonTower6F.asm

@@ -40,6 +40,10 @@ PokemonTower6FDefaultScript:
 	ld a, SCRIPT_POKEMONTOWER6F_MAROWAK_BATTLE
 	ld [wPokemonTower6FCurScript], a
 	ld [wCurMapScript], a
+
+	ld hl, wGenderFlags
+	set 1, [hl] ; set flag to force female gender for Cubone mother
+
 	ret
 
 PokemonTower6FMarowakCoords: