The best moveset for Mr Rime in the current competitive meta typically features the moves its most common attacks.
In the Pokémon Champions meta, Mr Rime can be countered by exploiting its weaknesses (bug 2x, dark 2x, fire 2x, ghost 2x, rock 2x, steel 2x) and using effective check/counter teams.
The best item for Mr Rime is typically Choice Scarf, based on high-level tournament and ladder stats.