Xerxes, Perfection

Indestructible, unblockable
When Xerxes enters the battlefield, tap all other creatures.
Whenever a creature would be untapped, its controller must pay {1} or it remains tapped. For each {1} paid in this way, put a +1/+1 counter on Xerxes.
Xerxes may only attack or block when it has nine or more +1/+1 counters on it.
All shall bow before us and know our glory.