Rite of Passage + Walking Ballista + Doubling Season

Rite of Passage

Walking Ballista

Doubling Season

How it works

1. Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to itself.
2. Rite of Passage triggers, 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.

By aiming Walking Ballista's own damage ability right back at itself, we trigger Rite of Passage to reward the creature with a +1/+1 counter for surviving that self-inflicted blow. Doubling Season steps in to amplify this entire loop, transforming that single added counter into two new ones. This means you net a positive growth of counters with every iteration, allowing you to easily stockpile an arbitrarily large number of +1/+1 counters on Walking Ballista before finally turning its deadly pings toward any other target.