Spontanzauber
Eine Kreatur deiner Wahl erhält bis zum Ende des Zuges -X/-X, wobei X gleich der Anzahl an Karten in deinem Friedhof ist.
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.