Spotter Thopter

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.

A prototype card is a colorless card in every zone except the stack or the battlefield, as well as while on the stack or the battlefield if not cast as a prototyped spell. Ignore its alternative characteristics in those cases. For example, while it's in your graveyard, Blitz Automaton is a colorless creature card with mana value 7. It can't be the target of Recommission, a spell that targets an artifact or creature card with mana value 3 or less in your graveyard.

Use Spotter Thopter's power at the time its triggered ability resolves (not the time it triggered) to determine the value of X. If Spotter Thopter is no longer on the battlefield at the time the ability resolves, use its power as it existed the last time it was on the battlefield.

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.

The prototype ability functions in any zone that the spell could be cast from. For example, if an effect allows you to cast artifact spells from your graveyard, you could cast a prototyped Blitz Automaton from your graveyard.