Toxic Spikes are terrible in this meta by the way. Fire-types are immune due to Flying being included, while Grass-types absorb them due to Poison being included. So basically, they only hit pure Water-types.
Fire-types actually seem OP to be honest. Being a Fire-type grants you immunity to Burn, Paralysis (due to Electric becoming Fire), Spikes/Toxic Spikes/Sticky Web (due to Flying becoming Fire), and trapping effects (due to Ghost becoming Fire). That might be balanced out by a weakness to the omnipresent Return/Frustration, though. Water, by comparison, gets the short end of the stick, with its only innate immunity being Freeze. Grass is immune to Poison and to Powder-based moves, but is trapped by Magnet Pull.
Psyshock is now almost pointless, as the blobs resist it; just use Psychic or Moonblast instead. Although, Psyshock still hits Heatran harder, so there's that at least. Secret Sword is even more pointless than Psyshock, as blobs resist it and Heatran is immune.
Flash Fire, Volt Absorb, Lightning Rod, and Motor Drive now make you immune to Seismic Toss, since it's now a Fire-type move. This means that Heatran walls, and is in turn walled by, pink blobs. Incidentally, the blobs are now SR-weak, so they might actually not be as good as they once were.
Justified triggers when hit by any damaging Water-type move. That's kind of neat, to be honest.
Rattled triggers when hit by any damaging move, period. lol.
Talonflame is kind of bad offensively, as both of its STAB typings turned into Fire and it has basically no coverage. Granted, Gale Wings working with any Fire-type move is pretty neat as well, since it does give Talonflame priority on Will-O-Wisp and Bulk Up. It actually has better overall bulk than Sableye, and like Sableye has priority Will-O-Wisp and priority recovery. Plus it resists SR, while Sableye is neutral. That said, lack of priority Taunt kind of sucks, as does lack of Knock Off, and the fact that Talonflame has a Water weakness while Sableye has no weaknesses.
Now back to theorymon:
Mega Gallade looks kinda scary.
Water/Fire
- Swords Dance
- Close Combat [Fire]
- Return [Water]
- Earthquake [Grass]/Shadow Sneak [Fire]
Diancie now has dual Physical STAB (Diamond Storm/Return) and dual Special STAB (Earth Power/Moonblast) along with STAB Psyshock, but still sucks due to not having a single Fire-type move other than Hidden Power. Damn it Diancie, can't you be good in an OM? Well, okay, your Mega form was good in Stat Switch, but then you got banned and you weren't even good in Stat Switch Ubers! Eh, I guess there's always Inheritance at least.
And now for some implementation questions:
— Should Water Absorb, Dry Skin, and Storm Drain grant immunity to Dark Void? I don't know if these abilities trigger from the move Soak normally, but if they do then it sets precedence for Dark Void to possibly be nullified. Notably there's no ability that grants immunity to Dark, and thus no precedence for whether Dark-type status would be affected by a Dark immunity, nor if only certain Dark-type status moves would be affected and which those would be.
— Should Sap Sipper be triggered by Stealth Rock and Toxic Spikes when switching in? In standard, Sap Sipper is triggered by Spore, Sleep Powder, and Stun Spore (all Grass-type status), so this seems like it might be a logical extension as Stealth Rock and Toxic Spikes are Grass-type hazards that factor resistance (Stealth Rock)/immunity (Toxic Spikes).