You could keep the same idea, but modify the mechanism:
Since you should have a ton of animals roaming around as your main army, let the worldspell cause them to breed (all animals spawn a copy of themselves, instead of all units spawn a wolf).
If the combining mechanic of the wolves is extended in some manner to the other animals, this would certainly be a powerful late game worldspell, but not so late that fully combined animals aren't strong enough to be a threat, and an equally viable early-mid game worldspell, not exactly useful before turn 50 while you have scant few total animals, but potentially worthwhile if you have 5 wolves and one is VERY highly promoted, copy that guy and you can rush an extra Civ.