The leaves growing on Sceptile’s body are very sharp edged. This Pokémon is very agile—it leaps all over the branches of trees and jumps on its foe from above or behind.
– Pokémon Omega Ruby Pokédex
Mega Sceptile is Grass/Dragon type instead of pure Grass. Not sure what makes it dragon, it doesn’t look very dragon-like to me. It’s only one of 2 Grass/Dragons, the other being Alolan Exeggutor.
Its ability is Lightning Rod, probably because its tail looks like a lightning rod. But it doesn’t really need immunity to Electric type attacks, since Grass/Dragon is 4x resistant to Electric. I guess it could be useful in double battles, to protect its partner.
Stat-wise, it has more Speed, Attack, and Sp Attack. It does learn a Dragon move by level-up, Dual Chop.