Mystery Booster 2

Walking Ballista

Walking Ballista enters with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on Walking Ballista.
Remove a +1/+1 counter from Walking Ballista: It deals 1 damage to any target.

Fallout

Assaultron Invader enters the battlefield with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on Assaultron Invader.
Remove a +1/+1 counter from Assaultron Invader: It deals 1 damage to any target.

Secret Lair Drop

Jumpstart 2022

Walking Ballista enters the battlefield with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on Walking Ballista.
Remove a +1/+1 counter from Walking Ballista: It deals 1 damage to any target.

Double Masters

Magic Online Promos

Aether Revolt Promos

Aether Revolt

Walking Ballista enters the battlefield with X +1/+1 counters on it.
{4}: Put a +1/+1 counter on Walking Ballista.
Remove a +1/+1 counter from Walking Ballista: It deals 1 damage to target creature or player.