Rite of Passage + Walking Ballista + Estrid's Invocation

Rite of Passage

Walking Ballista

Estrid's Invocation

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 Estrid's Invocation 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.