If you hack in a Volcanion, the raid would probably be pretty easy. Immune to Water Moves, 4x resists Ice, 2x resists Bug with a beefy 120 Defense stat and STAB Fire Moves off of a 130 Special Attack stat.
Okay, actual talk: there's a potentially risky way to oneshot the raid. I was considering Sun as an option; it weakens Samurott's Water attacks and strengthens the Fire Moves it'll be weak to. Here's my suggestion:
It'd be nice if it could use Sun as a raw attack enhancer and as a way to boost its Special Attack, but Game Freak probably decided that wasn't a good idea. Thankfully, both Sun and Electric Terrain can be up simultaneously, which allows this:
+4 252+ SpA Quark Drive Iron Moth Helping Hand Overheat vs. -2 0 HP / 0 SpD Tera Bug Samurott in Sun: 11552-13592 (3490 - 4106.3%) -- guaranteed OHKO
That's a fair amount of support (Sun/Electric Terrain/Helping Hand/two turns of Quiver Dance boosts alongside a Weakness Policy activation/Acid Spray on Samurott), but it gets the job done assuming Samurott has no EVs. If it does, another use of Acid Spray will give it the oomph needed.
As I was writing this I reminded myself of another very power Fire-type option this game provided, one that takes a turn less of setup because it gets Nasty Plot:
+4 252+ SpA Beads of Ruin Chi-Yu Helping Hand Overheat vs. -2 0 HP / 0 SpD Tera Bug Samurott in Sun: 11538-13574 (3485.8 - 4100.9%) -- guaranteed OHKO
Of course, both of these options are assuming Samurott won't have Drill Run as an option. It would still be doable if it had them, but would be riskier.
Tar Shot is also a fairly good move for a oneshot strategy, if you can get a Coalossal to survive long enough to use it. This might enable you to use Flamethrower over Overheat to avoid the miss chance.
Anyway those are my ideas, maybe someone with a little more experience with this can refine it/find the best Pokémon for it.