Enchantment, 1U (2)

When a player casts a spell, sacrifice Standstill. If you do, each of that player's opponents draws three cards.
"You learn a lot in no time when you're about to get your neck snapped."
—Dack Fayden
Illus. Matt Stewart

10/4/2004: It only works once. If someone casts another spell after it triggers, but before that trigger resolves, then it will trigger again. The first time one of these triggers resolves, it will be sacrificed for the full effect. Any additional triggers on the stack will do nothing when they resolve because you will be unable to sacrifice it additional times.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander