"Fear not what's under the bed. The toys are watching."
—*Beyond the Great Henge*

Workshop Elders

Artifact creatures you control have flying.
At the beginning of combat on your turn, you may have target noncreature artifact you control become a 0/0 artifact creature. If you do, put four +1/+1 counters on it.

March of the Machine Commander

The Brothers' War Commander

Throne of Eldraine

An artifact that becomes a creature due to Workshop Elders can't attack unless you've controlled it continuously since your turn began.

If another effect later causes the artifact to become a creature and sets its power and toughness as it does so, that creature will have that base power and toughness; it won't be 0/0. Notably, crewing a Vehicle does not set its power and toughness, so a Vehicle's base power and toughness remain 0/0 if you crew it.

The effect of Workshop Elders's triggered ability lasts indefinitely. It doesn't wear off during the cleanup step.