It's easy to describe Electivire in two words: GLASS CANNON. 123 Attack is nothing to laugh about, especially when it's on the opposite side of the field, and even more so when this thing is carrying Focus Punch. Electivire can blow holes in the opposing team, but he's so easy to revenge kill it doesn't seem to be worth the slot in yours. BUT, he's a late game sweeper for a reason: He only does his job once the threats are gone. So, to even TRY to use Electivire, get rid of everything that could possibly carry a powerful physical move, then you're free to bring in the beast and destroy everything your opponent has left with no major complications. This guy can KO around 2 Pokémon before going down, which is really good by UnovaRPG competitive standards.
Basically, to use Electivire, get rid of anything that's even remotely dangerous to him and leave only your opponent's support Pokémon. Then, Electivire is free to play around.
Pretty much any Ground-Type walls Electivire to a certain extent, because of their STAB Earthquake and since Electivire lacks the moves to cover them up, aside from a neutral, non-STAB, Focus Punch, he can't get rid of them quickly enough. Krookodile, for example, is Electivire's nightmare, with his high attack and Ground-Type (And thanks to UnovaRPG's single-type mechanics, Krookodile doesn't have his usual Fighting weakness), he can take everything E-Vire throws at him and retaliate with a STAB Earthquake, most likely OHKOing the Electric Juggernaut and ruining your foe's plans.