Whenever a battle takes damage, whether through direct damage spells or by attacking it with creatures, you remove that many defense counters from it
Aim for 3040 actual zombies in a 100-card Commander deck so your tribal lords and whenever a zombie dies payoffs stay live, then fill the rest with ramp, removal, card draw, and lands
As you can see above, there are plenty of ways to build up your devotion count quickly so that on turn five, even with only two of the above options on the battlefield already, you will be draining your opponent for 6 life or more
Legendary Planeswalker - Tezzeret Draw (CTRL to add secondary) Finisher Kappa Cannoneer Improvise (Your artifacts can help cast this spell
It also gives attackers pseudo-vigilance, letting you remove from combat a creature after its dealt damage and youre in your end of combat phase