
Artifact Creature — Construct
This creature enters with X +1/+1 counters on it.
: Put a +1/+1 counter on this creature.
Remove a +1/+1 counter from this creature: It deals 1 damage to any target.
0/0

Similar counter-removal pinger combo piece for direct damage.

Colorless X-cost artifact creature with +1/+1 counters.

Classic infinite combo partner with Ballista for unlimited damage.

Combos with Ballista for infinite damage via undying.

Colorless creature that pings any target each turn.

Pumps Ballista's counters for more removable ammo.

Counter-based creature that can move counters for utility.
→ Infinite damage, Infinite lifegain, Infinite lifegain triggers
→ Infinite damage, Infinite +1/+1 counters on a creature
→ Infinite death triggers, Infinite ETB, Infinite LTB
→ Infinite damage, Infinite lifegain, Infinite lifegain triggers
→ Infinite damage, Infinite lifegain, Infinite lifegain triggers
→ Infinite damage, Infinite +1/+1 counters on creatures you control
If Walking Ballista has been dealt damage or had its toughness reduced by an effect, this limits how many times you'll be able to remove +1/+1 counters from it in a single turn. For example, if it has three +1/+1 counters on it and has been dealt 1 damage this turn, it will be destroyed immediately after you activate the ability a second time and you won't be able to activate it a third time.
A casting cost of means that you pay twice X. If you want X to be 3, you pay
to cast Walking Ballista.