Here's what's going on: Mewtwo ex is a card that already exists in the game in several forms
IMPORT & EXPORT Already tracking elsewhere
Thanks to the rounded down wording, your opponent is always left with at least one creature, so they can always keep their best creature alive
With that in mind, I could see Zell easily finding a home in a Gruul or even Red/Green/x Commander deck that wants to play lots of lands that provide additional value beyond simply tapping for mana
Aside from counterspells and fast creatures, efficiency is going to be your next play
Id want to add Delayed Blast Fireball, Wild-Magic Sorcerer, and Nalfeshnee, plus combat tricks that cantrip, like Expedite, Crimson Wisps, and Might of the Meek, to help draw and exile cards