They can have ultimate abilities, but they generally dont win the game without some help
In this Collector Booster, Sauron sealed away the most incredible cards to grace Middle-earth: foils, Showcase cards, Borderless cards, and more
Either they take the damage, or they lose life blocking
But you do want to avoid the three common ways custom cards get ruined: Use high-quality art Bigger is better
The controller of that creature then gains life equal to its power, which means you can sometimes save yourself with this - or save an ally
Auntie Ool, Cursewretch Auntie Ool, Cursewretch is among the narrower options on the list since its card draw is restricted to your ability to put -1/-1 counters on creatures, but that's far from hard