So if you can select the opponents ability (which to me isnt hitting all /possible/ mons super effective, so i don't like this solution) an energy ball, mud shot, soak octillery almost does it, but paras line must not have dry skin, and you cant touch arceus. I think this is probably the solution the question asker is looking for though, and I'm going to show pretty conclusively that it can't otherwise be done.
There are four ways to change the opponents type:
1) Soak
2) Forest's Curse
3) Trick or Treat
4) Skill Swap + some type changing ability (color change easiest)
Any of these 4 methods needs to be able to hit pokemon they don't affect supereffective and hit all affected pokemon for supereffective with 2 coverage moves.
Case 1 (soak): Immune pokemon: Arceus, Paras line, Croagunk line, Chinchou line, Gastrodon line.
So requirements of 2 move coverage are: one of the two moves must be fighting type to hit arceus, so the pokemon must have an ability that lets it soak immune pokemon other than arceus (mold breaker) and then any move super effective against pure water (which, the only pokemon (basculin) with soak and mold breaker does not get outside of hidden power), or a move that hits all water mons, and the above listed lines all super effective. There is no overlap among their weaknesses, although freeze dry does come close, so it is NOT possible with soak.
Case 2 (Forest's Curse): Immune pokemon: all dualtyped pokemon with grass type already.
Requirements for this one are pretty easy: 2 move coverage that hits all grass/X dualtypes or grass/x/y triple types super effective. Obviously one of these moves must be one of bug, poison, flying, ice and fire type, as these are the full list of moves super effective on grass. So lets look for common threads in resistances to each:
Bug resists: steel, fire, flying. Clearly not possible to hit all three of these types super effectively in one move, Bug as primary coverage can't work.
Poison resists: Steel, rock, ghost, poison. Again, clearly not possible to hit all these types in one move, although ground hits all but ghost (although ground doesn't really work because of immunities anyways)
Flying resists: Steel, rock, electric. The only shared weakness is ground, but there are pokemon with these types immune to ground (rotom, skarmory, etc).
Ice resists (freeze dry assumed since its best): ice, fire, steel. There is no shared weakness between these types.
Fire resists: Fire, water, rock. There is no shared weakness between these types.
Therefore, Forest's curse can not be used.
Case 3 (Trick or Treat): Immune pokemon: all dualtypes with ghost already.
This one is fairly easy to disprove. It can't be done without fairy coverage to hit spiritomb and sableye, thus one move is needed to hit all pokemon when ghost type is slapped on. Ghost doesn't work because of normal types, dark doesn't work because of fairy types.
Case 4 (Skill Swap + color change): Immune pokemon are aegislash, shedinja, arceus.
Arceus again mandates fighting coverage, and you can run dark, ghost or fire coverage to hit aegislash and shedinja. Dark is the only coverage move that allows you to hit the opponent with super effective fighting afterwards, but this combination breaks down when running into spiritomb and sableye, so it is not possible.
So unless anyone has a solution that uses some other way I can't think of to change the opponent's type, there is definitely not a solution
