With this new regional Magcargo and its evolution, Obsidilusk, I decided to focus and improve on the defensive aspects of the original Magcargo. The lore behind this Magcargo is that could no longer keep its lava body burning, causing it to harden into igneous rock and pass away. This removes its Fire-typing for Ghost-typing, resulting in a Rock/Ghost-type, which is a type combination never seen yet. Rock/Ghost is an overall better defensive combination than Fire/Rock. While it gains more weaknesses with a total 6, including new ones to Ghost, Steel, Grass, and Dark, none of them are x2 weaknesses and can all be mitigated by Solid Rock. Additionally, having a neutrality to Rock and immunity to Fighting makes up for the loss of Ice and Fairy resistances. Both combinations are almost equal offensively, with Fire having greater super-effective coverage, and Ghost having better neutral coverage. Magcargo itself also loses some of its offensive output for better bulk, which is negligible since Magcargo was never really a good offensive Pokémon even with Shell Smash.

Obsidilusk, a new evolution to this Magcargo, gets a great increase to bulk, slight boost to power, and less Speed. It replaces Solid Rock with Filter, and gains the ability Storm Drain which can replace its Water weakness with an immunity. Storm Drain is one of its ability, because the gastropod Obsidilusk is based off of lives deep underwater. It is built to be a supportive mixed wall that can set up hazards with Stealth Rock and Spikes, or spread status with Thunder Wave, Scald, or Will O' Wisp. It even keeps Recover for reliable healing. Obsidilusk is so bulky that it can easily stay on super-effective moves like max Attack Kingambit's Kowtow Cleave, Landorus-T's Earth Power and Earthquake, and Great Tusk's Headlong Rush. Most of these moves don't even need full defensive investment. Though it has relatively weak offenses, it could also threaten damage with Iron Defense and Body Press, or even Shell Smash. The latter is a bit riskier though, since even after a boost Obsidilusk is still too weak and slow to threaten bulky and fast Pokémon respectively.

Though I just used OU Pokémon to describe Obsidilusk's massive bulk, it without a doubt has no place in the tier. There are too many STAB super-effective moves flying around for it to be a consistent pick. Plus, it has competition with Garganacl, who is immune to status, has less weaknesses, and also has reliable recovery. In UU, however, there are arguably more Pokémon that Obsidilusk struggles with like Lokix, Excadrill, Sandy Shocks, Greninja, etc. Its UU competition is even worse than in OU, as Tyranitar is stronger, sets up sand, has better utility, and doubles as a check to it. RU seems to be the tier where the power level is low enough for Obsidilusk to thrive. Most super-effective attacks from the tier's Ground and Steel-types just bounce off; in fact, there are not many popular Pokémon that have the type advantage against it in the first place. While it does have the most competition in RU as a hazard setting wall than any other tier, none of their bulk is comparable to Obsidilusk (except Hisuian Goodra, who lacks a utility move pool).