Sp. Attack: 75
Sp. Defense: 95
Serperior's not really an outstanding Pokémon. While 75/95/95 defenses might seem at the very least decent, and 75/75 Attack stats are not that bad for a Stage 2 Pokémon, you'll soon notice the BIG problem with Serperior in UnovaRPG: It's movepool. It's ENTIRE UnovaRPG (usable) movepool consists of only 4 types: Grass, Normal, a single Poison move in Toxic, and a single Flying move in Aerial Ace. That's HORRIBLE for a Stage 2 Pokémon, let alone a STARTER. You can run a mixed wallbreaker set with Leaf Storm, Leaf Blade, Giga Drain and Aerial Ace, but trust me, you're not gonna accomplish anything with it. Not even if you replace Leaf Blade with something as powerful as Solarbeam. Its defenses aren't going to get you anywhere either, Serperior can be 2HKO'd by an Azelf's Flamethrower. AZELF. Not STAB, only super-effective, and Serperior goes down. Although Giga Drain is a pretty good move with the potential to make Serperior stay in longer, but again, its defenses are nothing spectacular to really take advantage of it.
Seriously, if I were you, I'd search for another Grass-Type. ANY other Grass-Type works. Probably even Sunflora.
With 75/95/95 defenses, which is by no means bad, just average, it's not that hard to KO Serperior. Pretty much any super-effective move has the potential to take down Serperior in 3-4 hits tops. And with 75/75 offensive stats plus poor coverage, it's even easier to wall. Any Steel- or Poison-Type (Or even Grass-Type, if the trainer chose to replace Aerial Ace with Toxic) can take all of Serperior's hits and fire back for the kill.