My game just crashed when in the middle of a double battle between a Haunter and Nuzleaf and two Wingulls. It gave me this error message:
Script 'PokeBattle_MoveEffects' line 7154: NoMethodError occured. undefined method 'effects' for nil:NilClass
I think this was after both Wingulls had died and the Nuzleaf was trying to attack no target.