"Let the light scour away your imperfect flesh."
—Heliod

Sunfall

Exile all creatures. Incubate X, where X is the number of creatures exiled this way. (Create an Incubator token with X +1/+1 counters on it and "{2}: Transform this artifact." It transforms into a 0/0 Phyrexian artifact creature.)

March of the Machine Promos

March of the Machine

Exile all creatures. Incubate X, where X is the number of creatures exiled this way.

If Sunfall resolves but doesn’t exile any creatures, you’ll incubate 0, creating an Incubator token but putting no +1/+1 counters on it. It will still have the ability to transform, but you might need to figure out how it’s going to survive first.