Timid or Jolly depending on whether you want to use Leaf Blade or Leaf Storm as your main attack (obviously DW versions would be Timid always carrying boosting Leaf Storm). Basically you want to preserve its best (and pretty much only redeeming) stat in its speed. Max IV max EV positive speed natured Serperior (when you get it) is faster than the same conditions (max speed) Scolipede whereas the same situation but neutral speed nature doesn't even let you outspeed max speed positive natured base 99s (aka Genesect) and above, which is sad when there are some very dangerous pokemon in that 99-112 speed range, so definitely get +speed nature.
His stats are pretty much balanced. He's not a strong Sp. Attacker (just Giga Drain, Leaf Tornado, and Energy Ball I think if you're not using Perversity Snivy) so I'd say Jolly. Abuses his high Speed, doesn't mess with his decent Defense stats, and Coil+Leaf Blade ain't too bad. Though if you prefer Sp. Attacks over Physical Attacks then go with Timid and use Calm Mind over Coil. Growth isn't too good because his attack stats aren't too high so.....best to focus on one or the other.
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