Creatures with power less than Howlgeist’s power can’t block it.
Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner’s control with a +1/+1 counter on it.)
The comparison of power is performed only when blockers are declared. Increasing the power of a blocking creature (or decreasing the power of Howlgeist) after this point won’t cause any creature to stop blocking or become unblocked.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.