One of the most expensive pieces of the Memento engine is Memento Angwich
Having these abilities stapled to a cheap creature provides plenty of options: You can attack or kill a problematic blocker or save a creature
When the ability resolves, Tree of Perdition's toughness becomes the targeted opponent's former life total and that player gains or loses an amount of life necessary so that their life total equals Tree of Perdition's former toughness
Here is where it gets interesting
W/U Flash, which really seems to be gaining traction, proved to be a challenge, so coming up with a better solution against that deck will probably help
Deathleaper, Terror Weapon Ikoria gave us a bunch of cool keyword lords like Frondland Felidar and Quartzwood Crasher, and Deathleaper, Terror Weapon is basically your choice of haste or flash lord