MewPluff is really only viable when run with trainer-lock, as otherwise everything will be able to setup normally, meaning Mew just can't keep up with it's 60HP against all the powerhouses nowadays(despite maybe outspeeding them). Jamming an opponent's setup by either a). Trainer locking b). Sludge Dragging/Catchering and/or c). Fast KO's of key parts are the only way Mew can compete with all the other decks.
Your best matchup would be Gothitelle, and your worst matchups would be ZPST and Donphan. While Stage 1 Rush can also be a big threat, if you can jam their communications fast enough, as well as Judge'ing them early on, you could have a good chance at taking the lead and nab yourself the win.
ReshiPhlosion/Tyram, Blastoise/Floatzel, Megazone, KYJ, and most rogue decks will be 50/50 or 40/60, but it all depends on how consistent your deck runs, ''luck of the draw'', and the level of the players. MewPluff (or Mewbox depending on your complete list) is still a decent enough deck to hold it's ground, but I doubt it will claim any ''big'' tournament. Try it for yourself, and see how it works for you. Mew's biggest asset is being able to go many ways, and this flexibillity is really the only selling point it has in today's meta (of course, for those nit-pickers, the free retreat helps too).
On your point of view on Eviolite; yes, it will help Mew. But when you take into account that stuff like Reshiram, Zekrom, Thundurus, Tornadus, Magnezone, and even AbillityBoar can OHKO it without effort, do you really want to include it? Sure, it helps against stuff like Donphan (or even a stray Ninetails, or something like that), but with only 20 HP left, Mew isn't going to do much either way. In that aspect Tornadus is the way better option here; it has a ''bulky'' 110HP, is a basic as well, requires no extra type of energy, and smacks 80 as well as powering up your Mews and/or other attackers. Also don't forget, if you're going for the trainer-lock, your own Eviolites will be stuck in your hand as well... Don't forget that Mew running Vileplume can include Sunflora for speed issues, which then opens the way to including Yanmega Prime (which also resists Donphan, hits for 70 on the active or can snipe for 40 anywhere you'd want).
Good luck with the deck, and feel free to PM me if you want more advice/feedback!