I’d say this one falls more under the category of a Natural born or Regional based Delta.
Larvitar that live close to volcanoes, and endure the heat of surrounding magma lakes eventually adapt and gain this form.
Constant exposure heat tempers this Pokemon’s rocky skin into a fusion of volcanic metal and obsidian, this causes the Pokemon to gain the Steel typing upon evolving into it’s later stages.
Upon reaching it’s final evolution this Pokémon gains the new ability Ash Fall. This ability summons a new weather type called Fire Rain this strange weather occurs when burning ash falls from volcanic clouds, this new weather then deals damage to each non Fire or Rock type Pokémon equal 1/16 of its maximum HP, and 1/8th of it’s max HP in the case Grass or Steel types, this summoned weather usually last around 5 turns before dissipating. It also boosts the special attack stat of Fire type Pokémon , and halves the amount of HP recovered from certain recovery moves.
Larvitar
Fire/Rock
Pupitar
Fire/Steel
Tyranitar and M-Tyranitar
Fire/Steel
Bonus Shinies for the final stages.
Let’s call this color palette Fel Fire green…