Unstoppable Ash

The defensive trigger is the trick that turns this from a Champion-tax body into a combat-math problem for your opponent. Champion mechanics ask you to exile a creature you already control and hand it back when the Treefolk leaves play, so the steep cost here is the tempo loss of feeding it a Treefolk or Warrior on the way in. What you buy with that exile is an attack step where blocking stops working: any creature you control that gets blocked swells by +0/+5, which means trades you initiate flip into one-sided kills, and the opponent's chump-blocking math collapses. Note the wording carefully, because it is the whole engine: the bonus fires on becoming blocked, not on attacking, so it rewards you for sending in creatures the defender feels obligated to stop, and it stacks across multiple attackers in the same combat. A swarm of small bodies that would normally die to blockers instead survives and lives to swing again, while the 5/5 trample on top punishes any attempt to gang-block the Ash itself. It is built around the idea that the defending player's most basic resource, the decision to block, can be made actively unprofitable, and it does that work for an entire board rather than one creature.