Enchantment, 4R (5) Whenever a creature with power 5 or greater enters the battlefield under your control, you may have Where Ancients Tread deal 5 damage to target creature or player.1 "Never subtle nor cryptic is the reckoning of the mighty." —Mayael the Anima
Illus. Zoltan Boros & Gabor Szikszai
10/1/2008: The ability checks that creature's power only once: when that creature enters the battlefield. The trigger checks a creature's initial power upon being put on the battlefield, so it will take into account counters that it enters the battlefield with and static abilities that may give it a continuous power boost once it's on the battlefield (such as the one on Glorious Anthem). After the creature is already on the battlefield, boosting its power with a spell (such as Giant Growth), activated ability, or triggered ability won't allow this ability to trigger; it's too late by then. Once the ability triggers, it will resolve no matter what the creature's power may become while the ability is on the stack.