So I leaned into being an Archenemy with a full-blown board control deck that knocks players out with 3 hits from my Slurm Queen, group slug () damage effects, or proliferate shenanigans
Plant/Pendulum/Effect
Nature's Will can technically do it too, but it untaps lands after damage, which is too late for Hellkites trigger unless you already have an extra combat to set it up
I can't more strenuously recommend Bant (or at least, not Sultai )
However, most decks need a way to remove the opponent's stadium and stop them from gaining an advantage, and stadium cards can often be difficult to search from the deck
No matter what cards were designed for them, with The Ur-Dragon and O-Kagiachi headlining the same deck side-by-side, one of them was going to feel underwhelming, and its definitely O-Kagiachi