Bug, Grass, Electric and Dark huh..
A Flying/Ground Type should do the job, its a legendary, so yeah...
You said Numel? Numel evolves into Camerupt and then Camerupt recieves an Mega, but you get that later on in-game.
For Camerupt you should have this moveset:
Camerupt@Camerutite (or something..)
Anger Point (HA) --> Sheer Force
Quiet Nature (+ Sp. Atk, -Speed)
EVs: 252 Sp. Atk/ 126 Sp. Def / 126 Def
- Eruption
- Earth Power
- Fissure
- Hidden Power (Grass or Electric)
Camerupt covers your Bug, Grass, and Water Types. M Camerupt is awesome too, but the sacrifice for speed makes it super slow..
Slowbro also has a chance of Mega Evolving, too.
Slowbro@Slowbrotite
Regenerator (HA) --> Shell Armor
Modest Nature (+Sp. Atk, -Atk)
EVs: 252 Sp. Atk/126 Sp. Def/126 Def
- Surf
- Psychic
- Flamethrower
- Signal Beam
Another, yet awesome Mega.