See support for details
It can be used not only in a defensive way, clearing annoying ETBs or powerful abilities, but also in an offensive way, making Deaths Shadow 13/13 or Kroxa, Titan of Deaths Hunger a two mana 6/6
Blastoise takes longer to evolve, and would need to be benched briefly while you get your ducks in a row, beefing up its energy with some Misty flips or pure patience, using another card upfront as an aggro starter or damage sponge
This big green gorilla man looks equally good in rainbow as evidenced by the Rillaboom VMAX Rainbow Rare
Something like Sensei's Divining Top can make sure you draw instants and sorceries for your turn plus some kind of sacrifice outlet to use the demon each turn, and make room for a new one would go a long way too
In my experience, it's always harder than I want it to be to pull this off