It seems very unlikely that the consistency you lose from playing 20 extra cards will decrease your odds of winning by 10% or more, which would mean even discounting any specific Yorion, Sky Nomad synergy, it would be correct for a lot of decks to add some extra cards to meet the Bird Serpent's companion restriction
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Craterhoof Behemoth One of the best green pump spells, Craterhoof Behemoth is the classic top end of elves and other go-wide ramp decks that even has an Eternal format deck named after it: Turbo-hoof
Elspeth Tirel, Patron of the Kitsune, Sun Droplet, Spirit Loop, Angelic Chorus Special bonus: this is one of the few decks that you can justify running Angelheart Vial
Now that we answered that question, lets move on to the next one: How do we win
It will release in our Ascended Heroes special set on January 30th