The Mind Automaton

Indestructible
At the beginning of your upkeep, put a thought counter on The Mind Automaton.
{1}, Remove a thought counter from The Mind Automaton: Target opponent mills 5, then create a 2/2 Mind Witherling creature token with: 'Whenever an opponent mills a card, this creature deals 1 damage to any target.'
The mind of a genius, trapped for eternity.