Assemble

Assemble is a keyword action introduced as a joke in Future Sight and related to Contraptions. It was greatly expanded upon in Unstable, where it was one of the main silver-bordered mechanics. Contraptions may be assembled by players and/or Creatures (Riggers).

Description
To assemble a Contraption means putting the top card of your Contraption deck face up onto one of your three sprockets.

There is no functional difference between players assembling a contraption, and creatures assembling a contraption. However, Steamflogger Boss only cares about Contraptions assembled by creatures.

Reassemble
Reassemble is a related keyword, featured on Suspicious Nanny and Cogmentor. It means (to gain control) and move it onto (another) one of your sprockets. You don't have to advance it in the normal direction.

History
It was stated that this mechanic and Contraptions were meant as a joke. Forsythe's statement ensured that players wanted it and they've bugged Mark Rosewater about it ever since. Thus, Rosewater vowed to figure out contraptions' design before he would retire.

Rulings

 * If a card instructs you or a creature you control to assemble a Contraption, but your Contraption deck is empty, then nothing happens.