(This is my first actual post, so I hope i'm doing this right)
I'd like to suggest a nominee:
Aerodactyl(Mega) ===> B+/A Rank: Aerodactyl is already known for its high base 130 speed, somewhat decent defenses at 80/65/75 and a base attack of 105. I feel that it's attack is what held it back before, but in Mega Form with a hard hitting 135 base Attack and huge 150 base Speed, this pokemon can do work, and do work very well. With 80/85/95 bulk, this thing can devastate with little to no defensive support. Setting in a Light Clay Light Screen before hand would make this thing hard to 1HKO with special attacks, and it's typing really leaves it with 2 major physical weaknesses: Steel and Rock, both of which are most of the time slow. Granted it's ability Tough Claws is almost completely wasted on STAB moves, since it learns no Rock moves with Physical contact, and Acrobatics can't be done in normal cirumstances to its fullest extent with a Mega, leaving Mega Aerodactyl with Aerial Ace, Sky Drop, and Fly, this ability gives a much needed boost to the elemental fang moves and Steel Head, an ever important move to have with Fairy Types like Florges completely walling Special Attacks. I've done multiple sweeps using Mega Aerodactyl, and with my Florges setting up Light Screen Before hand, this prehistoric monster has survived Scald from a Greninja with slightly under half HP. Although it's ability requires some thinking when creating a moveset, this Mega is flat out deadly.
