Ignoring the Implications of what it'd do to the Eeveelution's movesets, How would an Eevee with the following moveset do theoretically.
Eevee @ Salac Berry
Adaptability
Modest/Timid
Conversion
Fire Blast
Hydro Pump
Thunder
Obvious plan is Conversion, bank on taking 2/3's of Eevee's health out, and then start rapid-firing the corresponding elemental move. Is there any competitive use to it or would it be purely novelty? I'd inquire as to what that'd do to the Evolutions too, but such is a question for another thread...
Actually, given it's Sp.Attack is Weaker than it's Attack, perhaps Flare Blitz/Aqua Tail/Volt Tackle? Swapping the nature and EVs to match of course.