Regal Ancestor Spirit

{1}{g}{u}{t}: Sacrifice another creature. Put X +1/+1 counters on Regal Ancestor Spirit,
where X is equal to the sacrificed creature's power.

Remove X +1/+1 counters from
Regal Ancestor Spirit:
You may cast a spell with mana value equal to the
number of counters removed this way without
paying it's mana cost.