>>96337963
Basically nothing. A turn 2 kill is challenging but turn 3 is very doable with fetches and any batch of ramp cards.
My most recent line was
Turn 1
>Exploration
Turn 2
>Tifa
>Summer Bloom
>Instill Energy
2^5 = 32 haste/trample commander damage. OTK. Instantly hellbent and do nothing after as a result.