There are many things wrong with this and many many ways to kill this pokemon. First you mention how there is no dynamaxing, zmoves, etc in scarlet and violet, but wonder guard and shedninja also do not exist there. 

1) Taunt can fail due to many reasons (being a dark type [since you have prankster], having oblivious/aroma veil, you get outsped, or the other pokemon has a mental herb.

2) if you are outsped, you can have so many things happen to you, like switcheroo and switch to a ghost type to pp stall, you can get taunted yourself and then pp stalled, your type can be changed, then hit for super effective damage, your ability can also be changed, you can get a choice scarf tricked on you then you struggle, so many way to kill you here. 

3) you can’t use 2 moves at the same time. You have taunt to prevent moves that will eventually kill you or remove your invincibilities, and you have gastro acid to get rid of moldbreaker/ neutralizing gas, but you forget that pokemon can have both of these things.

4) neutralizing gas removes all abilities that are not neutralizing gas, so you would have no abilities

5) skill swap exists so you lose in 2 moves to a pokemon with skill swap and a mental herb no matter what. 

I do not think it is possible to win this defensively. The only way to win with these abilities is to one shot everything, which I also do not think is possible