This is an instant staple
You may even want to bring along a stack of lands, or similar, to serve as a proxy for your opponents deck entirely
On top of the 10/10 flying body that Ureni comes with, you also have a commander with protection from both white and black, the two colors with the most single-target removal in the game
Given the format-warping power of the Evoke Elementals from Modern Horizons 2, that seems to be a fair assessment
The reason that people are not playing with Heros Downfall as much as they probably should be is that the 1BB mana cost is extremely taxing on a mana base that also wants to have 2UU for Jace, Architect and 1UWW for Supreme Verdict on turn 4
This attribute boost completely warps the resource math of a match, transforming low-cost characters into highly dangerous offensive threats