Creatures you control have skulk. (They can't be blocked by creatures with greater power.)
: Creatures you control get +1/+1 until end of turn.
Skulk matters only as blockers are chosen. Modifying either creatureâ€™s power after blockers are chosen wonâ€™t cause the attacking creature to become unblocked.
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 wonâ€™t be blocked, but it wonâ€™t deal combat damage and wonâ€™t trigger any abilities that trigger when combat damage is dealt.