As an additional cost to
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) this spell,
sacrificeTo sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent they don’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action. (CR 701.21) X Contraptions.
AssembleAssemble 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. (CR 701.45) X plus one Contraptions. (To
assembleAssemble 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. (CR 701.45) a Contraption, put the top card of your Contraption deck face up onto one of your sprockets.)