Mesmeric Trance

Pitch a dead card, draw a fresh one, repeat for a single blue mana: the rummaging half of this enchantment works exactly the way a filtering engine should, and on its own it would run all game. Cumulative upkeep is what sabotages it. The mechanic charges an escalating toll every turn the permanent survives, so the first activation arrives cheap and the fifth or sixth comes wrapped in a stacking tax you pay just to keep the thing on the battlefield. The trouble is that the toll climbs while the payoff stays frozen: each loop still nets the same one-for-one rummage, no matter how much mana you sink into staving off the sacrifice. A repeatable card-filtering effect wants longevity, and a drawback that punishes longevity is precisely backwards for it. That mismatch runs through much of Ice Age's signature mechanic, which tried to balance strong effects by making them temporary rather than conditional, and which Wizards eventually moved away from on permanents players actually want to keep. Later filtering enchantments solved the problem by charging a flat activation cost and trusting the card disadvantage to do the balancing. This one bills you twice over: once in cards discarded, once in an ever-rising upkeep, all for a payoff that never grows.