Rootwire Amalgam

Casting a prototyped spell isn't the same as casting it for an alternative cost, and an alternative cost may be applied to a spell cast this way. For example, if an effect allows you to cast an artifact card without paying its mana cost, you could either cast Blitz Automaton normally, or as a prototyped spell.

When cast as a prototyped spell, that spell has the mana cost, power, and toughness characteristics shown in its colored, secondary text box rather than the normal values of those characteristics. Its color and mana value are determined by that mana cost. The permanent that spell becomes as it resolves has the same characteristics. If the spell leaves the stack in any other way, or the permanent it becomes leaves the battlefield, it immediately resumes using its normal characteristics.

When casting a prototyped spell, use only its prototype characteristics to determine whether it's legal to cast it. For example, if Blitz Automaton is exiled with the last ability of Chandra, Dressed to Kill, you would be able to cast it for {2}{R} (because it's a red spell), even though you wouldn't be able to cast it as a colorless spell for its normal cost.