Ages ago, a party of elves took cover to let one pass. They're still waiting.

Endless Wurm

Trample
At the beginning of your upkeep, sacrifice this creature unless you sacrifice an enchantment.

The List

Urza's Saga

Trample
During your upkeep, sacrifice an enchantment or sacrifice Endless Wurm.

You choose whether to sacrifice an enchantment or not on resolution. If not, then you sacrifice this card. You can choose to not sacrifice an enchantment if you no longer control this card on resolution.