Voodia, the Methodical

Whenever you cast an instant spell any time a
sorcery could have been cast, it gains casualty X,
where X is Voodia's power. (As you cast that spell,
you may sacrifice a creature with power X or greater.
When you do, copy the spell and you may choose new targets for the copy.)
Whenever an opponent casts a spell any time a
sorcery couldn't have been cast, counter it unless
they sacrifice a creature.