MTG: Can I sacrifice as many creatures as I want?

Question

I have seen a few instant spells, which say to Sacrifice a creature and "something happens"

when I play the Instant spell, am I able to sacrifice as many creatures as I want to the spell, or does "a" restrict me too 1 creature?

thanks

Answer 1

You may only sacrifice as many creatures as the spell tells you to. Some say to sacrifice "a" creature, meaning one. There are a couple that say to sacrifice "all" creatures you control.

Answer 2

Usually when a card says to "Sacrifice a creature," it means that you are only allowed to sacrifice one creature per spell cast.  Other cards will usually instruct you to either sacrifice -a- creature you control, to sacrifice any number of creatures you control, or to sacrifice ALL creatures you control.  Certain cards have erratas on them which may differ with what I'm explaining now.

Answer 3

If the instant says something like "Sacrifice a creature: gain 1 life." on an instant, you can only sacrifice one creature because you're playing a spell. However, if that shows up on a creature, you can use that as many times as you want during your turn because it's an ability--this means that as long as that creature is out, you can use its ability as many times as you can afford to. But back to instants...you will know if you can sacrifice as many creatures as you want because the text will say "Sacrifice X creatures: gain X life.", or something to that extent. Then the card leaves it up to you how much you want to sacrifice and how much you will gain from it.