Making a few more nominations.
B- -> C+ Alakazam, how you've fallen from grace... I'd just repeat myself, as everything's already been said, but it has so much trouble revenge killing stuff in this Generation with faster Pokémon like Greninja and priority users like Mega Pinsir, (Mega) Scizor and Talonflame all over the place. All in all, Mega's more worth it, but that is explained below.
Alakazam should drop to C+.
B- -> B The problem with Mega Alakazam...is that it's a Mega Pokémon. It has a sizable opportunity cost, but is far better than regular Alakazam. With 175 Special Attack and 150 Speed, Mega Alakazam is an absolutely devastating offensive force. Gary2346 has already explained why this thing is good, so I can't really add much else, but the fact that, with the movepool and
immense Special Attack and Speed that allow it to run a Modest nature without a care (it outspeeds +1 Jolly Mega Tyranitar to give an example), but being held back by being a Mega Pokémon, I still think
Mega Alakazam deserves a solid B Rank. I'm fine with
B-, but still prefer to see it a bit higher, just because it can be really effective once it gets going.
C -> C+ Salamence may be horribly outperformed in the current OU metagame, but honestly, it's more outclassed than outright bad. Dragonite has more bulk with Multiscale and Mega Charizard X has two awesome STABs to use, but Salamence can still perform mixed DD sets quite well. It's just often discredited due to being outclassed, like Thundurus-T, who is B-. Therefore, I support
Salamence for C+ Rank.
A- -> B+ As has been brought up before, Latias just has a hard time keeping up with this offensively inclined metagame and its sibling Latios has a large advantage with its much higher Special Attack. Don't get me wrong, Latias is still good, but not as effective as it used to be/could be because of the metagame.
Latias for B+.