Cetoddle

Powder Snow + Avalanche and Body Slam

Powder Snow is a great Fast Attack, providing high energy generation and decent damage. Ice Shard offers more balanced parameters, but the extra damage it deals compared to Powder Snow is not worth the significant amount of energy generation loss. Tackle is outclassed.

Avalanche is one of the best Charged Attacks in PvP and benefits from Cetoddle's STAB. Body Slam is another excellent move, being incredibly cheap and providing good damage for its cost; it also provides some coverage against Fire- and Water-type opponents. Heavy Slam is useless outside of nailing certain Pokemon with double weakness to Steel.

Great League: 3 / 5

Mono Ice isn't a particularly amazing typing, but Cetoddle can make it work thanks to its incredible moves. However, it does have stiff competition from other Ice-type Pokemon such as Froslass, Dewgong, and Alolan Sandslash, all of which possess useful secondary typings and greater overall coverage. Keep in mind that Cetoddle needs to be fully XLed and Best Buddied to reach the Great League CP cap, where it maxes out at 1487 CP at Level 51.

Ultra League: 0 / 5

Cetoddle caps at Great League CP; you don't want to use it in the Ultra League.

Master League: 0 / 5

Hydrogen bomb vs coughing baby.