Мгновенное заклинание
Целевое существо получает -X/-X до конца хода, где Х — количество карт на вашем кладбище.
Festive Funeral is still on the stack while you determine the value of X. It doesn't contribute to the value of X.
The value of X is determined only as Festive Funeral begins to resolve. The target creature's power and toughness won't change if other cards are put into your graveyard later in the turn.