Biggest example I can think of Jade Golem.
I’ve always thought jade golem was pretty cool, but try as I might I’ve never been able to make it work. You’re in theory building your jade golems up, meanwhile your zerg opponent is pouding you into the dirt, or you can’t draw the right card as there are so few to draw so while you should be able to beat someone who’s not zerging you, in reality it’s at best 50% which makes it’s so disappointing.