DNA Donors: Metagross / Banette
Offspring name: Banegross
New type: Ghost / Steel
New base stats: 72 / 135 / 97 / 89 / 86 / 87 (+10 Atk, +10 Special Defense, +20 Speed)
New ability and desc:Hard Body (Insomnia + Clear Body) - Stat drops inflicted either by moves, abilities or status are ignored.
Notable moves: Meteor Punch, Iron Head, Bullet Punch, Shadow Sneak, Shadow Claws, Phantom Force, Sucker Punch, Knock Off, Zen Headbutt, Ice Punch, Thunder Punch, Earthquake, Gunk Shot, Pursuit, Hammer Arm, Hone Claws, Agility, Destiny Bond, Will-O-Wisp, Magnet Rise, Pain Split, Disable, Thunder Wave
Role identification: It's immune to stat drops of all kind, it has Aegi's typing and 2 STAB priorities and it can reliably go Scarfed thanks to its nice 87 Speed.
DNA Donors: Mega Metagross / Banette
Offspring name: Mega Banegross X
New type: Ghost / Steel
New base stats: 72 / 145 / 117 / 99 / 106 / 127
New ability and desc:Tough Claws
Notable moves: Meteor Punch, Iron Head, Bullet Punch, Shadow Sneak, Shadow Claws, Phantom Force, Sucker Punch, Knock Off, Zen Headbutt, Ice Punch, Thunder Punch, Earthquake, Gunk Shot, Pursuit, Hone Claws, Agility
Role identification: This one is like a Ghost/Steel version of MegaGross, but it has double priority STAB, Sucker Punch, Knock Off and far better Speed.
DNA Donors: Metagross / Mega Banette
Offspring name: Mega Banegross Y
New type: Ghost / Steel
New base stats: 72 / 185 / 107 / 99 / 106 / 97
New ability and desc:Prankster
Notable moves: Destiny Bond, Will-O-Wisp, Magnet Rise, Pain Split, Disable, Thunder Wave, Taunt, Confuse Ray, Meteor Punch, Iron Head, Bullet Punch, Shadow Sneak, Shadow Claws, Phantom Force, Sucker Punch, Knock Off, Zen Headbutt, Ice Punch, Thunder Punch, Earthquake, Gunk Shot, Pursuit, Hammer Arm, Hone Claws, Agility
Role identification: Welcome the monster: MHeracross's Attack (the highest base Attack stat in OU, before abilities and items), 72/107/106 bulk, decent 97 Speed (and priority Agility/Rock Polish to double it), Prankster to setup with priority or to inflict statuses to the opponent, STAB priority for both its types and Sucker Punch, Knock Off to stall-break or nullify Choichers... What else? Oh, Phantom Force can break Protect and similar moves and it has Aegislash's typing.