Skeleton Key

Text:

Equipped creature has skulk. (It can't be blocked by creatures with greater power.)
Whenever equipped creature deals combat damage to a player, you may draw a card. If you do, discard a card.
Equip

Rulings:

• 4/8/2016 Skulk matters only as blockers are chosen. Modifying either creature’s power after blockers are chosen won’t cause the attacking creature to become unblocked.
• 4/8/2016 If you cause a creature to have 0 power or less, use the actual value (which may be negative) to determine whether it can block or be blocked. A creature with skulk and 0 or less power most likely won’t be blocked, but it won’t deal combat damage and won’t trigger any abilities that trigger when combat damage is dealt.