One of the big reasons why Sultai Mutate scored so low in so many categories is that the deck is built around a brand new mechanic that doesn't have any support from the past 25 years of Magic , which limits the number of good on-theme reprints and even keeps many of the most powerful mutate cards out of the deck since Wizards presumably wanted to save them for Ikoria proper
Would this be the next Izzet template
Boilerbilges Ripper Four generic, one red creature Human Assassin 4/4 Common When Boilerbilges Ripper enters, you may sacrifice another creature or enchantment
Incidentally, exile effects like these are also excellent against Deathmist Raptor, which is another major player in Standard alongside Hangarback Walker
That prize goes to Circle of Protection: Artifacts
For example, you could be in either Undercity or Lost Mine of Phandelver, but not both