Gearmaster's Workshop

Improvise (Your artifacts can help cast this spell.
Each artifact you tap after you're done activating
mana abilities pays for {1}.)
Tinker {2} ({2}{t}: Create a 1/1 Gearbeast artifact
creature token with "{t}, Sacrifice this creature: Add {c}.")
{t}, Sacrifice Gearmaster's Workshop: Create an
X/X Gearbeast artifact creature token, where X
is the number of artifact creatures you control.