Mutate hasn't had a huge impact on Standard—certainly not compared to the other big mechanic from Ikoria, companion. Lurrus of the Dream-Den, Gyruda, Doom of Depths, Yorion, Sky Nomad and Keruga, the Macrosage either slotted into existing decks or spawned their own archetypes, while the Apex cycle of creatures have yet to find a place, and other mutate support cards like Pollywog Symbiote have been totally neglected.

At least part of mutate's relative lack of success may be due to how strong removal is in Ikoria Standard. Mutate works best when you can keep stacking a creature with more and more mutations, triggering all the other mutations each time for repeated value. Heartless Act can seriously flummox that plan at instant speed for just two mana, leaving you with nothing for your multi-turn investment.

#####CARDID=14942#####

Thankfully, there's a solution. Kaya's Ghostform has a fun interaction with mutate cards: if you slap it on a heavily mutated creature, when your opponent kills it, all the mutations return to the battlefield as creatures. That means your opponent has to choose between giving you an army and letting your monstrosity mutate more, drawing cards, killing creatures and draining life. Not bad for a "junk" common.