A Careful nature (+SPDEF, -SPATT) would best suit a Specially-Defensive tank, which...Electivire could technically pull off. I'll include an Elekid set if you were wanting to do Little Cup battles. It would help to know whether its ability is Motor Drive (Elekid: Static) or Vital Spirit, but I'll manage.
T-Punch/Wild Charge (STAB)
Power-Up Punch/Charge (Raises uninvested Attack stat)
Sleep Talk (Stall)
If its ability is Vital Spirit, it can't use Rest, so do this instead:
Ice Punch (or any coverage move: EQ, Brick Break, etc.)
You could also switch out Charge for another attacking move so it would be able to hold Assault Vest (to further boost SPDEF).
For Elekid, keep the same moves, but give it Eviolite.
Honestly, if you don't want to make it into a tank, I'd just use it to trade for another shiny/legendary/mythical.