Config for Dark Void being only usable by Darkrai

data/battle_scripts_1.s

@@ -411,6 +411,7 @@ gBattleScriptsForMoveEffects::
 	.4byte BattleScript_EffectSteelBeam               @ EFFECT_STEEL_BEAM
 	.4byte BattleScript_EffectExtremeEvoboost         @ EFFECT_EXTREME_EVOBOOST
 	.4byte BattleScript_EffectTerrainHit              @ EFFECT_DAMAGE_SET_TERRAIN
+	.4byte BattleScript_EffectDarkVoid                @ EFFECT_DARK_VOID
 
 BattleScript_AffectionBasedEndurance::
 	playanimation BS_TARGET, B_ANIM_AFFECTION_HANGED_ON
@@ -775,9 +776,7 @@ BattleScript_EffectPhotonGeyser:
 BattleScript_EffectAuraWheel: @ Aura Wheel can only be used by Morpeko
 	jumpifspecies BS_ATTACKER, SPECIES_MORPEKO, BattleScript_EffectSpeedUpHit
 	jumpifspecies BS_ATTACKER, SPECIES_MORPEKO_HANGRY, BattleScript_EffectSpeedUpHit
-	printstring STRINGID_BUTPOKEMONCANTUSETHEMOVE
-	waitmessage B_WAIT_TIME_LONG
-	goto BattleScript_MoveEnd
+	goto BattleScript_PokemonCantUseTheMove
 
 BattleScript_EffectClangorousSoul:
 	attackcanceler
@@ -889,9 +888,7 @@ BattleScript_BothCanNoLongerEscape::
 BattleScript_EffectHyperspaceFury:
 	jumpifspecies BS_ATTACKER, SPECIES_HOOPA_UNBOUND, BattleScript_EffectHyperspaceFuryUnbound
 	jumpifspecies BS_ATTACKER, SPECIES_HOOPA, BattleScript_ButHoopaCantUseIt
-	printstring STRINGID_BUTPOKEMONCANTUSETHEMOVE
-	waitmessage B_WAIT_TIME_LONG
-	goto BattleScript_MoveEnd
+	goto BattleScript_PokemonCantUseTheMove
 
 BattleScript_EffectHyperspaceFuryUnbound::
 	attackcanceler
@@ -3020,6 +3017,11 @@ BattleScript_MoveMissed::
 	waitmessage B_WAIT_TIME_LONG
 	goto BattleScript_MoveEnd
 
+BattleScript_EffectDarkVoid::
+.if B_DARK_VOID_FAIL >= GEN_7
+	jumpifspecies BS_ATTACKER, SPECIES_DARKRAI, BattleScript_EffectSleep
+	goto BattleScript_PokemonCantUseTheMove
+.endif
 BattleScript_EffectSleep::
 	attackcanceler
 	attackstring
@@ -9783,3 +9785,11 @@ BattleScript_TargetAbilityStatRaiseRet::
 	call BattleScript_StatUp
 BattleScript_TargetAbilityStatRaiseRet_End:
 	return
+
+BattleScript_PokemonCantUseTheMove::
+	attackstring
+	ppreduce
+	pause B_WAIT_TIME_SHORT
+	printstring STRINGID_BUTPOKEMONCANTUSETHEMOVE
+	waitmessage B_WAIT_TIME_LONG
+	goto BattleScript_MoveEnd

include/constants/battle_config.h

@@ -91,6 +91,7 @@
 #define B_METRONOME_MOVES           GEN_LATEST // This config will determine up to which generation will Metronome pull moves from.
 #define B_TELEPORT_BEHAVIOR         GEN_LATEST // In Gen7+, starting with Pokémon LGPE, Teleport allows the user to swap out with another party member.
 #define B_BEAT_UP                   GEN_LATEST // In Gen5+, Beat Up uses a different formula to calculate its damage, and deals Dark-type damage. Prior to Gen 5, each hit also announces the party member's name.
+#define B_DARK_VOID_FAIL            GEN_LATEST // In Gen7+, only Darkrai can use Dark Void.
 
 // Ability settings
 #define B_EXPANDED_ABILITY_NAMES    TRUE       // If TRUE, ability names are increased from 12 characters to 16 characters.

include/constants/battle_move_effects.h

@@ -392,6 +392,7 @@
 #define EFFECT_STEEL_BEAM                   386
 #define EFFECT_EXTREME_EVOBOOST             387
 #define EFFECT_DAMAGE_SET_TERRAIN           388 // genesis supernova
+#define EFFECT_DARK_VOID                    389
 
 #define NUM_BATTLE_MOVE_EFFECTS             389
 

src/data/battle_moves.h

@@ -8339,7 +8339,7 @@ const struct BattleMove gBattleMoves[MOVES_COUNT_Z] =
         #else
             .accuracy = 80,
         #endif
-        .effect = EFFECT_SLEEP,
+        .effect = EFFECT_DARK_VOID,
         .power = 0,
         .type = TYPE_DARK,
         .pp = 10,