Metagame name: Weaknessmons(better name pending)
Metagame premise: Pokemon can only learn moves for the types that they are weak to, without factoring in abilities.
Examples: Gholdengo is weak to Fire, Ghost, Dark, and Ground moves. Therefore, Gholdengo would only learn Fire, Ghost, Dark, and Ground moves. Existing movepool is ignored.
Example 2: Rotom-Wash is immune to Ground via Levitate, but the Electric/Water typing makes it weak to Grass and Ground. Therefore, Rotom-Wash gets Grass and Ground moves.
Potential bans and threats:
:gholdengo: :dragapult: :gengar: Ghost types get a big boost in this format, as they can use their best STAB options, unlike a lot of other mons.
:chi-yu: :palafin: :magearna: Normally broken mons like these may be balanced in this metagame, as they lack reliable STAB options and can end up being weaker than the competition.
As for bans, probably the standard OU banlist with these changes:
- Dragapult
+ Chi-Yu
+ Palafin
+ Magearna
+ Annihilape(?)
Questions for the community: Are there any broken moves that should be banned day 1? Is Gholdengo gonna be overwhelming?
Another thing which differentiates this from other metas is the complete lack of Normal-type moves: no more Substitute, Protect, Swords Dance, Shell Smash, Explosion, Fake Out, Extreme Speed, Revival Blessing, Transform, Encore, Boomburst, etc.
Grass types have a lot of potential here. Among other things, they have access to Sticky Web, Toxic Spikes, Toxic, Mortal Spin, Defog, Roost, Will-O-Wisp, U-turn, Defend Order, Tail Glow, and Quiver Dance. Also, Ghosts and Dragons have access not only to STAB moves but to good boosting options as well (Nasty Plot and Dragon Dance respectively).
To answer your questions: I would definitely ban Last Respects, and probably also Rage Fist and Astral Barrage, otherwise Ghosts will be way too powerful. I don't think Gholdengo should start on the banlist, but I do think it should be on the watchlist, since it still has most of what makes it good in OU (Good as Gold, Nasty Plot, reliable recovery [Shore Up], and Ghost STAB), plus now it blocks all hazard removal (since Tidy Up and Court Change are Normal moves and thus unusable) and there are few mons apart from ghosts that can hit it with supereffective STAB.