Quoted By:
For stats and ability, I don't care all that much. Pokémon games are deliberately easy and competitive play doesn't interest me. Obviously I'd appreciate if Mega Meganium was strong, even if just to laugh at the naysayers, but it doesn't matter that much to me. I care more about its design and lore, and even if I don't like the mega's design, it sure is a good thing Meganium is already the perfect Pokémon. The good thing about megas is that they're optional, and you can just use the base form if you don't like em, unlike with regional variants.
With all that said, assuming abilities are in this time, Triage would be cool, like many have been saying. Really, anything that amplifies its role as a support mon and/or makes it a bit more versatile. More move options are also good.