This isn't gonna go well, but I guess life is about risks.
Attack:
Original Pokemon: Regigigas
New Pokemon: Regigeist
Type:
Abilities: Slow Start
Stats: 110 /
150 / 110 / 120 / 110 / 70 [BST: 670]
Weight: Same
Movepool Changes: + Calm Mind, Chilly Reception, Fire Blast, Giga Drain, Ice Beam, Icy Wind, Poltergeist, Psychic, Psyshock, Shadow Ball, Shadow Sneak,
Thunderclap, Trick, Trick Room, Vacuum Wave
Thunderclap: Electric-type Special Sucker Punch clone.
Height: Same
Flavor / Explanation: Ghost (Ugly) Regi.
Competitive Role: Physical leaning mon in terms of stats, but special leaning in terms of movepool due to CM, and Thunderclap is a funny new move, so lol.
Defense:
Original Pokemon: Registeel
New Pokemon: Regiwheel
Type:
Abilities: Clear Body | Psycho Engine (HA)
Psycho Engine: Rattled + Summons Psychic Terrain if HP reaches 1/4 or less.
Stats: 80 / 80 /
150 / 110 / 80 / 80 [BST: 580]
Weight: Same
Movepool Changes: + Ally Switch, Calm Mind, Expanding Force, Extrasensory, Future Sight, Magic Room, Psychic, Psychic Terrain, Psyshock, Shadow Ball, Trick, Trick Room, Volt Switch, Wonder Room, Zen Headbutt
- Body Press, Dynamic Punch, Focus Blast, Focus Punch, Hammer Arm, Hone Claws, Ice Punch, Mega Punch, Metal Claw, Power-Up Punch, Shadow Claw, Superpower, Thunder Punch
Height: Same
Flavor / Explanation: Psychic (Wheel) Regi.
Competitive Role: Rattled + Weakness Policy Psychic mon with actual defense to absorb things like Knock Off and U-turn + Psychic Terrain in pinch to make revenge killing difficult.
Special Attack:
Original Pokemon: Regice
New Pokemon: Regifire
Type:
Abilities: Clear Body | Rocky Payload (HA)
Stats: 80 / 110 / 80 /
150 / 110 / 50 [BST: 580]
Weight: Same
Movepool Changes: + Earth Power, Fire Blast, Fire Punch, Flame Charge, Flamethrower, Flare Blitz, Heat Wave, Lava Plume, Meteor Beam, Morning Sun, Overheat, Power Gem, Sandstorm, Stealth Rock, Sunny Day, Will-O-Wisp
- Avalanche, Aurora Veil, Blizzard, Frost Breath, Hail, Ice Beam, Ice Punch, Icicle Spear, Icy Wind, Rain Dance
Height: Same
Flavor / Explanation: Fire (Crystal) Regi.
Competitive Role: Just a generic Meteor Beamer, nothing much else to say.
Special Defense:
Original Pokemon: Regirock
New Pokemon: Regifog
Type:
Abilities: Clear Body | Super Luck (HA)
Stats: 80 / 50 / 80 / 110 /
150 / 110 [BST: 580]
Weight: 0.1 kg
Movepool Changes: + Aeroblast, Air Cutter, Air Slash, Aromatic Mist, Blizzard, Defog, Fairy Wind, Focus Energy, Gust, Haze, Heat Wave, Hurricane, Icy Wind,
Megatornado, Mist, Rain Dance, Recover, Tailwind, Teleport, Twister, Whirlwind
- Bulldoze, Dig, Earthquake, Meteor Beam, Mud-Slap, Rock Blast, Rock Polish, Rock Slide, Rock Throw, Rock Tomb, Rollout, Sandstorm, Sand Tomb, Smack Down, Stealth Rock, Stomping Tantrum, Stone Edge
Megatornado: Flying-type Psycho Boost clone.
Height: Same
Flavor / Explanation: Flying (Fog) Regi.
Competitive Role: I was mainly thought about Eject Pack + Regenerator combo, but anaconja said this was broken, so I guess Regen has to go. In case you wonder, the new "gimmick" is that critical will ignore Megatornado's SpA drops.
And the last, but not least...
HP
OR Speed? Why not HP
AND Speed!

Original Pokemon: Regieleki / Regidrago
New Pokemon: Regidraeki
Type:
Abilities: Clear Body | Adaptability (HA)
Stats:
140 / 50 / 100 / 50 / 100 /
140 [BST: 580]
Weight: Average of both.
Movepool Changes: Combined of both Eleki and Drago.
+
Dragon's Cage: Dragon-type Thunder Cage clone.
+
Electron Energy: Electric-type Dragon Energy clone.
+ Power Shift
Height: Uh.....
Flavor / Explanation: It's obvious, isn't it?
Competitive Role: A fast tank that utilizes its bulk to chip with Thunder/Dragon's Cage. Dragon/Electron Energy with Power Shift aren't something to be underestimated either.