The Kaladesh update bulletin includes the following line:
Also on the subject of power and toughness, we have a new rule that if a creature has no power or toughness, that value is 0. This can happen if you manage to get a crew ability to animate a non-Vehicle artifact.
The newly defined rule itself says:
208.5 If a creature somehow has no value for its power, its power is 0. The same is true for toughness.
The update bulletin doesn't mention what cards could possibly enable this to happen though, and I can't for the life of me figure out how this gets set up. Is it some combo involving Necrotic Ooze or something?
How can I crew a non-vehicle to arrive at this situation?