Spotter Thopter

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.

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.

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.