Would you like to see a Mega Vileplume?
Yes and no… I mean, Vileplume is my favourite Pokémon so, like, if you want to give her cool stuff, go right ahead, but I don’t know if the pile of extra stats associated with mega evolution necessarily solves the problems that she has. With the exception of Slowbro, Sableye and Aggron, most top-tier mega Pokémon are offensive powerhouses, and that’s not really what Vileplume is trying to do anyway. I think her real problem is that her hidden ability (Effect Spore) is just bloody useless, and her regular ability (Chlorophyll) is amazing but completely mismatched to her role. You could use mega evolution to cheat in a replacement ability, I suppose, but honestly I would much rather just add a second regular ability; most Pokémon have two, and giving Vileplume something a) really strong and b) different from what other Grass-type supporters have would, I think, just about do it.