Only did two this round so I'll repost this with another mon for it support! It's win-win, non-Mega supports Aurortoise, Mega supports Stoutdrill! It's weather mon for all teams!
DNA Donors: Manaphy / Tyranitar
Offspring Name: Manatar
New typing: Water/Dark
New base stats: 100/117/105/117/100/100 (BST 639, SpA + 20, Spe +20)
New ability and desc: Hydro Stream: Summons rain upon switch in for 5 turns, 8 with Damp rock. (This is a different ability to Drizzle in the same way that Pure Power is a different ability to Huge Power).
Notable Moves: Hydro Pump, Dark Pulse, Tail Glow, Thunder, Ice Beam, Energy Ball, Heart Swap, Waterfall, Crunch, Pursuit, U-Turn, Dragon Dance, Stone Edge, Ice Punch, Thunder Punch, Stealth Rock, Superpower, Iron Head, Rest, Sleep Talk, Toxic, Scald, Rock Polish
Role identification: A storm is brewing. At the forefront, we have Manatar, a second rain setter for the OU tier, meaning that rain teams no longer have to rely solely on Politoed for passive rain setting. Furthermore, Manatar outclasses Politoed in every stat, bar Special Defence which it ties on, and surpasses it in movepool as well, allowing it to run offensive or defensive sets far greater than Politoed ever could have dreamed (bar Perish Song, I suppose). Manatar's offensive potential is great on both the Physical and Special sides, with moves such as Waterfall, Crunch, Pursuit, Hydro Pump, Scald and Dark Pulse for STAB (the Water moves of which are incredibly powerful in Rain) and a plethora of coverage moves, as well as Tail Glow, Rock Polish and Dragon Dance for set-up moves, boosted by solid 117/117/100 offences and 100/105/100 bulk. Speaking of which, this good level of bulk can allow Manatar to use a defensive set to increase its longevity and to be able to set rain many times throughout the game. The final, most notable tool in this pseudo-Drizzler's repertoire is U-Turn, which allows it to switch in, set rain, and then switch back out while gaining momentum for its team, making it exceptional on a rain team, allowing it support its team in more than just setting rain. Manatar works well with many other fusions, including SpartanMalice's Azumarill/Swampert, as well as other Swampertite fusions. It also helps Cofagreelix and Mega Aggrosaur V, who after abilities and in rain, are completely neutral to Fire-type attacks, relieving them of one of their weakness and allowing them to wall better than ever before. Other fusions, such as Joltlord, simply appreciate the boost to their Water-type attacks. This Pokemon is the start of a perfect storm of fusions, ready to take the meta by storm.
Mega Manatar (Tyranitarite)
New typing: Water/Dark
New base stats: 100/147/145/117/120/110 (BST 739)
New ability and desc: Sand Stream but it's not even Rock-Type
Notable Moves: Hydro Pump, Dark Pulse, Tail Glow, Thunder, Ice Beam, Energy Ball, Heart Swap, Waterfall, Crunch, Pursuit, U-Turn, Dragon Dance, Stone Edge, Ice Punch, Thunder Punch, Stealth Rock, Superpower, Iron Head, Rest, Sleep Talk, Toxic, Scald, Rock Polish
Role identification: Kind of missing the point of the original fusion, but it has good stats all round, making its set-up offensive sets even more impressive than ever. Can work as a sand-setter for use with Sand Rush Excadrill and the like. OR NOW FOR STOUDRILL, AH, WINK WINK NUDGE NUDGE
Parents: Aurorus/Blastoise
Shared Egg Group: Monster
Offspring Name: Aurortoise
New typing: Water/Ice
New base stats: 111/90/96/102/108/78 (BST 585)
New ability and desc: Hydrate: Turns Normal-type moves into Water-type moves and powers them up (EDIT: By 1.33x, sorry for any confusion).
Notable Moves: Hyper Voice, Ice Beam, Freeze Dry, Thunderbolt, Aura Sphere, Dark Pulse, Rapid Spin, Fake Out, Toxic, Scald
Role identification: As a new kind of -ate user, Aurortoise has a unique niche, the ability to user a
rain-boosted, Hydrate STAB Hyper Voice, something that's far from easy to tank, especially off a respectable 102 Special Attack Stat. It also gets this massive boost applied Fake Out and Rapid Spin, allowing it to revenge kill opponents in Rain and actually maybe deal damage while clearing hazards if you're lucky, with a decent 90 in Attack. Also, it can only be spin-blocked by Pokemon with Water Absorb/Storm Drain etc. Thanks to Aurorus, it also gets access to Boltbeam, boosting its coverage massively, as well as with its other coverage moves from Blastoise. Although its 78 Speed is a let down, It has nice 111/96/108 bulk to help it take damage as well as deal it, giving it survivabilty. While some may call these stats "average", what's that to a Pokemon with an -ate ability, semi-STAB BoltBeam and Rapid Spin?
Mega Aurortosie (Blastoisite)
Offspring Name: Mega Aurortoise
New typing: Water/Ice
New base stats: 111/110/116/152/118/78 (BST 685)
New ability: Mega Launcher
Notable Moves: Hydro Pump, Ice Beam, Freeze Dry, Thunderbolt, Aura Sphere, Dark Pulse, Rapid Spin, Fake Out, Toxic, Scald
Role identification: Mega Aurortoise is quite different from it's base form. While it loses out on Hydrate Hyper Voice, it gets massive stat boosts and a rain-boosted STAB Hydro Pump off a 152 Special Attack stat is still going to hurt a lot. It still has Rapid Spin and BoltBeam, so it maintains its good coverage and utility, and Mega Launcher gives Dark Pulse and Aura Sphere a chance to shine. It gets much improved bulk, now at 111/116/118, making 78 Speed much more justifiable. All together, Mega Aurortoise, while losing out on its unique ability, gains a lot of other buffs making it as powerful a tank as its base form, if not more so and, if paired with Manatar, more than capable of nuking entire unprepared teams single-handedly.