Haste (This creature can attack and as soon as it comes under your control.)

At the beginning of the end step, sacrifice Arc Runner.

Protean Hydra enters with X +1/+1 counters on it.

If damage would be dealt to Protean Hydra, prevent that damage and remove that many +1/+1 counters from it.

Whenever a +1/+1 counter is removed from Protean Hydra, put two +1/+1 counters on it at the beginning of the next end step.