Rite of Passage + Walking Ballista + Clever Impersonator

Rite of Passage

Walking Ballista

Clever Impersonator

How it works

1. Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to itself.
2. Rite of Passage and Clever Impersonator trigger, putting two +1/+1 counters on Walking Ballista.
3. Repeat an arbitrarily large number of times.
4. Move to the next turn, removing all damage marked on Walking Ballista.
5. Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to any target.
6. Repeat step 5 as desired.