Whenever a creature is exiled from the battlefield, put a +1/+1 counter on this creature
You don't have to be wearing the hat
What you are not seeing is that every time a new seller lists a Moat at a price near the Market Price, it sells, leaving behind cards with listed prices far above what the card will sell for
Being that it's a repeatable Mutate effect that just gets bigger and bigger, the effect could even bypass a Pacifism if you're going wide enough
This often means that nowadays, the most powerful cards for non-rotating formats are printed in a supplemental set (rather than in Standard)
Although there are five decks, four players is probably the sweet spot five player games will go longer, three player games will go faster (but have less of a multiplayer feel)