Earthquake is the classic, but here are similar spells which are good to know about: #25
If you play mainly in opponents turns, it has less effect(s) on you
We actually wrote a whole Commander Deck Tech about Karumonix, though, which will make his value far more clear than a single blurb could manage, so check it out if youre interested
You are going to distribute a massive amount of +1/+1 counters this way, so make sure you capitalize all of them with cards like Doubling Season and Branching Evolution
Part of the reason is just the sheer amount of excellent art in the set, which the publisher says contains the largest collection of Final Fantasy artwork ever in a single game. But another big reason are the goofs, which are deeply embedded into the mechanics of the popular trading card game
Things only get better when you consider the creature it can become