Potential Pokémon to add
Regidrago- UR to C- or C
Regidrago's Speed Tier, Terrible Movepool and inconsistency makes it much more niche compared to the other Dragon types in the tier. (Only being able to do Choice Band and Specs Sets effectively) But Regidrago's Power and Lack of Non-Fairy Check's on stall, gives it a niche.
I know steel Types exist, but a Modest Specs Dragon Energy 2OHKO almost every Steel Type in the tier. Which means most Pokémon can't switch into it without either dying or taking over 40-50%. (Tho, Not running Timid Makes you slower than Key Threats like Offensive Buzzwole, Bisharp and Volcanion)
Here's Some Calcs
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 252+ SpD Ferrothorn: 163-192 (46.3 - 54.5%) -- 60.5% chance to 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 0 HP / 4 SpD Bisharp: 335-395 (123.6 - 145.7%) -- guaranteed OHKO
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 252+ SpD Celesteela: 179-211 (44.9 - 53%) -- 88.3% chance to 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 4 SpD Blissey: 387-456 (54.2 - 63.8%) -- guaranteed 2HKO
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 4 SpD Toxapex: 370-436 (121.7 - 143.4%) -- guaranteed OHKO
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 136+ SpD Heatran: 191-225 (49.4 - 58.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 0 SpD Landorus-Therian: 606-714 (158.6 - 186.9%) -- guaranteed OHKO
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 40 HP / 104 SpD Melmetal: 309-364 (73.3 - 86.4%) -- guaranteed 2HKO after Stealth Rock
(Timed Regidrago can also do some of these Calcs)
So Pretty Much Against Stall, if the Player you're playing against doesn't have a Fairy type (Or The Fairy Type is dead) Regidrago will have an amazing time. Despite having 50 in Both Defenses, Regidrago is not that Frail, and can survive an attack and then OKHO or Deal Heavy Damage Back with Draco Meteor. (Here's some more Calcs)
252 SpA Heatran Earth Power vs. 0 HP / 4 SpD Regidrago: 170-200 (31.4 - 36.9%) -- 80.1% chance to 3HKO
252 Atk Zeraora Close Combat vs. 0 HP / 0 Def Regidrago: 204-241 (37.7 - 44.5%) -- guaranteed 3HKO
252 SpA Zapdos Hurricane vs. 0 HP / 4 SpD Regidrago: 301-355 (55.6 - 65.6%) -- guaranteed 2HKO
252+ SpA Choice Specs Volcanion Sludge Wave vs. 0 HP / 0 SpD Regidrago: 295-348 (54.5 - 64.3%) -- guaranteed 2HKO
252+ SpA Life Orb Sheer Force Nidoking Sludge Wave vs. 0 HP / 0 SpD Regidrago: 374-442 (69.1 - 81.7%) -- guaranteed 2HKO
252+ Atk Choice Band Bisharp Knock Off (97.5 BP) vs. 0 HP / 4 Def Regidrago: 436-514 (80.5 - 95%) -- guaranteed 2HKO
Regidrago last move doesn't really matter, but moves like Hyper Beam, Ancient Power or even explosion can help deal with Fairy Types.
Pokémon like Garchomp, Dragonite, Dragapult, and even Haxorus mostly outclasses Regidrago thanks to their Greater Consistency, Actual coverage, Better Speed Tier and being able to run different sets effectively. But Regidrago can do one thing the others can't do, destroy Stall.
The other's Need to use Sword Stance or Dragon Dance to even Reach Regidrago's level of power. when they're setting up, they can be burned, Intimated, Toxiced or Hazed, in Dragapult's case, It's Walled by Blissy and Sp Defensive Heatran.
So in a Nutshell, Regidrago instant power should give it a niche in OU
I mean no offense but you're really asking for Drago to be blacklisted at this point. It's been thoroughly discussed and the general consensus at least from the council was to keep it unranked.