Primeval Spawn

The spells are cast one after the other during the resolution of Primeval Spawn’s last ability. The one you cast last will be the first one to resolve.

As long as mana was paid for any cost to cast Primeval Spawn, it enters the battlefield as it resolves. It will not be exiled as it tries to enter the battlefield, even if its cost was reduced or a cost other than its normal mana cost was paid.

If a creature token that is a copy of Primeval Spawn would be put onto the battlefield, it’s put into exile instead and then ceases to exist. Creature tokens are never cast, even if the spell that created them was.

If you cast a spell without paying its mana cost, you can’t choose to cast it for any alternative costs. You can, however, pay any additional costs. If the spell has any mandatory additional costs, you must pay those.

If Primeval Spawn is exiled by its first ability as it tries to enter the battlefield, it goes directly to the exile zone without entering the battlefield first. Since it never enters or leaves the battlefield, its last ability won’t trigger.

Conversely, if an effect would cause Primeval Spawn to enter the battlefield as a copy of another permanent, it will enter the battlefield as a copy of that permanent whether or not it was cast or mana was spent to cast it.