It mimics some of the abilities of Ulamog, Kozilek and Emrakul, as per the name
Mutating a creature onto Ivy turns it into a token copy, giving you all sorts of potential for shenanigans, especially if you play a few copy spells and choose to make Ivy nonlengendary by placing the mutate creature on top of Ivy
Mila, Crafty Companion / Lukka, Wayward Bonder Mila, Crafty Companion grows your planeswalkers whenever opponents attack them and also draws you cards when your permanents are targeted
Youll also be more likely to immediately convert on Outcaster Trailblazers triggered ability to draw cards by plotting it and having more access to mana to immediately cast a large creature on a future turn
In some instances, there are other options that can fit really well into your deck
Youll require two undying creatures in play, sacrificing the first to put a -1/-1 counter on the other, effectively resetting the +1/+1 counter from the undying mechanic