Hippo, Stampede Rider

Whenever Hippo, Stampede Rider or another creature enters the battlefield, put a stampede
counter on each creature.
At the beginning of combat on your turn, if there
are 20 or more stampede counters on creatures,
each creature with a stampede counter on it deals damager equal to its power to each opponent,
then tap those creatures, they don't untap during
their controller's next untap step. Remove all
stampede counters from creatures.