Move-unique effect commands consistently go in engine/battle/move_effects/

engine/battle/move_effects/nightmare.asm

@@ -0,0 +1,38 @@
+BattleCommand_Nightmare: ; 37536
+; nightmare
+
+; Can't hit an absent opponent.
+
+	call CheckHiddenOpponent
+	jr nz, .failed
+
+; Can't hit a substitute.
+
+	call CheckSubstituteOpp
+	jr nz, .failed
+
+; Only works on a sleeping opponent.
+
+	ld a, BATTLE_VARS_STATUS_OPP
+	call GetBattleVarAddr
+	and SLP
+	jr z, .failed
+
+; Bail if the opponent is already having a nightmare.
+
+	ld a, BATTLE_VARS_SUBSTATUS1_OPP
+	call GetBattleVarAddr
+	bit SUBSTATUS_NIGHTMARE, [hl]
+	jr nz, .failed
+
+; Otherwise give the opponent a nightmare.
+
+	set SUBSTATUS_NIGHTMARE, [hl]
+	call AnimateCurrentMove
+	ld hl, StartedNightmareText
+	jp StdBattleTextBox
+
+.failed
+	call AnimateFailedMove
+	jp PrintButItFailed
+; 37563