A-Tier: I Have Slight Doubts, But Likely Eventually Biorhythm ($6) Golos, Tireless Pilgrim ($2) Iona, Shield of Emeria ($4) Sylvan Primordial ($2) Flash ($1.50) These five cards are powerful and potentially really annoying, but theres a lot to be said for each of these being totally fine
If Aerith Gainsborough is dealt lethal damage at the same time that you gain life, it will die before its second ability would resolve
I will play three turns against two tempo-centric decks: Humans and Mono-Red Prowess
Mutant is a broad enough creature type that this creature will get many triggers, and each of those triggers plays into all the strategies Ive mentioned before
Same with Scheming Symmetry
You need fewer cards in the graveyard per activation (albeit more specific cards), it has the same activation cost, it will typically deal more than two damage per activation, it will get larger over time, and it has menace