I've been messing around on the ladder under the alt End Of Story. Here are my thoughts on some of the megas I have seen/used.
Mega Absol: I really wanted to make this Pokemon work as I love the Magic Bounce ability, but it just isn't worth the Mega slot. Due to the reliance on Sucker Punch as STAB, it is very easy to play around. It will absolutely lose in a match against Roost Talonflame due to Sucker Punch's meager PP. It has no bulk, and can't switch into many hazard setters like Tyranitar, Mamoswine and Ferrothorn.
Mega Venusaur: This is far better than I expected. It can keep in check a ton of things, and just doesn't die. One of the best answers to Lucario, Azumarill and Greninja you could ever hope to get. STAB Sludge Bomb + poison chance puts in a lot of work, and unlike many other bulky Mega Pokemon it has good recovery between Leech Seed and Synthesis. I have stalled out Volcarona with this thing more than once. My personal favorite.
Mega Mawile: Can be a bit fiddly to play around, but on the whole it hasn't been too threatening. It's very slow, so if you have a decently fast Will-o-Wisp user you can usually play around it.
Mega Gengar: To be honest, you don't get many players on PS! who use Mega Gengar to its full capacity. But it's still completely broken in the right hands. It will always take down two or more Pokemon thanks to Destiny Bond. There's not much to say on this thing.
Mega Kangaskhan: Supremely bulky and will 2HKO Gliscor without an attack boost. You will see this more than any other mega, and for my money it's the one you should prepare the most for. It cannot be walled, but due to its lack of recovery you can steadily wear it down. Like Gengar, it will probably be banned.
Mega Absol: I really wanted to make this Pokemon work as I love the Magic Bounce ability, but it just isn't worth the Mega slot. Due to the reliance on Sucker Punch as STAB, it is very easy to play around. It will absolutely lose in a match against Roost Talonflame due to Sucker Punch's meager PP. It has no bulk, and can't switch into many hazard setters like Tyranitar, Mamoswine and Ferrothorn.
Mega Venusaur: This is far better than I expected. It can keep in check a ton of things, and just doesn't die. One of the best answers to Lucario, Azumarill and Greninja you could ever hope to get. STAB Sludge Bomb + poison chance puts in a lot of work, and unlike many other bulky Mega Pokemon it has good recovery between Leech Seed and Synthesis. I have stalled out Volcarona with this thing more than once. My personal favorite.
Mega Mawile: Can be a bit fiddly to play around, but on the whole it hasn't been too threatening. It's very slow, so if you have a decently fast Will-o-Wisp user you can usually play around it.
Mega Gengar: To be honest, you don't get many players on PS! who use Mega Gengar to its full capacity. But it's still completely broken in the right hands. It will always take down two or more Pokemon thanks to Destiny Bond. There's not much to say on this thing.
Mega Kangaskhan: Supremely bulky and will 2HKO Gliscor without an attack boost. You will see this more than any other mega, and for my money it's the one you should prepare the most for. It cannot be walled, but due to its lack of recovery you can steadily wear it down. Like Gengar, it will probably be banned.