Historical Rules · 12 July 2019
Rule 701.40a
Official source text from the 12 July 2019 Rules release
Assemble is a keyword action in the Unstable set that puts Contraptions onto the battlefield. Outside of silver-bordered cards, only one card (Steamflogger Boss) refers to assembling a Contraption. Cards and mechanics from the Unstable set aren’t included in these rules. See the Unstable FAQ for more information.