Myr Scrapling

Sacrifice Myr Scrapling: Put a +1/+1 counter on target creature.

Hangarback Walker

Hangarback Walker enters with X +1/+1 counters on it.
When Hangarback Walker dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on Hangarback Walker.
{1}, {T}: Put a +1/+1 counter on Hangarback Walker.

Nesting Grounds

{T}: Add {C}.
{1}, {T}: Move a counter from target permanent you control onto another target permanent. Activate only as a sorcery.

Steel Overseer

{T}: Put a +1/+1 counter on each artifact creature you control.

The Ozolith

Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.
At the beginning of combat on your turn, if The Ozolith has counters on it, you may move all counters from The Ozolith onto target creature.

Steel Dromedary

Steel Dromedary enters tapped with two +1/+1 counters on it.
Steel Dromedary doesn't untap during your untap step if it has a +1/+1 counter on it.
At the beginning of combat on your turn, you may move a +1/+1 counter from Steel Dromedary onto target creature.

Monoskelion

Monoskelion enters with a +1/+1 counter on it.
{1}, Remove a +1/+1 counter from Monoskelion: It deals 1 damage to any target.

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.