In b4 this thing becomes NUBL
Gen 8 NU

Regidrago @ Choice Specs
Ability: Dragon's Maw
EVs: 4 Def / 252 SpA / 252 Spe
Modest / Timid Nature
IVs: 0 Atk
- Dragon Energy
- Draco Meteor
- Dragon Pulse
- Ancient Power / Hyper Beam
This Pokemon is ridiculous. Having a strong move STAB in Dragon Energy when at full HP. Here is a Choice Specs set. Dragon Energy is incredibly powerful STAB at full HP, and when paired with Dragon's Maw coupled with Choice Specs, steel types are worn down by this move. Draco Meteor is also strong STAB and is used when Dragon Energy's power is less than the power of Draco Meteor. Dragon Pulse is used for well, more STAB since Regidraco doesn't have good special coverage. The last slot, honestly, is just there because Regidraco's special movepool is so bad(You literally don't get anything to deal super effective damage to fairy types. Not even its physical movepool has super effective fairy coverage for the fairy types in NU.). Ancientpower / Hyper Beam is just there to do some damage on fairy types I guess. Make sure to pair this with something that beats fairy types.
Calcs with Dragon Energy at full HP against the steel types in NU:
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 168 SpD Bronzong: 191-225 (56.5 - 66.5%) -- guaranteed 2HKO after Leftovers recovery
Possible damage amounts: (191, 193, 195, 198, 200, 202, 204, 207, 209, 211, 213, 216, 218, 220, 222, 225)
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 252 HP / 252+ SpD Escavalier: 175-207 (50.8 - 60.1%) -- 87.5% chance to 2HKO after Leftovers recovery
Possible damage amounts: (175, 177, 180, 181, 183, 186, 188, 189, 192, 194, 196, 198, 200, 202, 204, 207)
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 0 HP / 92 SpD Assault Vest Copperajah: 201-237 (52.2 - 61.5%) -- guaranteed 2HKO
Possible damage amounts: (201, 204, 206, 208, 211, 213, 216, 218, 220, 222, 225, 228, 230, 232, 234, 237)
252+ SpA Choice Specs Dragon's Maw Regidrago Dragon Energy (150 BP) vs. 212 HP / 0 SpD Eviolite Doublade: 295-348 (94.5 - 111.5%) -- 68.8% chance to OHKO
Possible damage amounts: (295, 299, 302, 306, 309, 312, 316, 319, 323, 327, 330, 333, 337, 340, 344, 348)
So, while Regidraco can't touch fairy types in NU, it can wear down steel types on its own.