Shark type attacks are strong against Water, Rock, and Shark type pokemon.
Shark type attacks are not very effective against Steel and Poison type pokemon
Shark type pokemon resist Fire, Water, Grass, Ice, and Fighting type pokemon
Shark type pokemon are weak to Electric, Steel, Poison, and Shark type pokemon
Electric type pokemon are immune to Shark type attacks
Changed types
Sharpedo: Shark-Dark instead of Water-Dark
Gible (and evolutions): Shark-Ground instead of Dragon-Ground
Barraskewda: Water-Shark instead of pure water
Basculegion: Shark-Ghost instead of Water-Ghost
Other Pokemon
Alternate form of Dreepy (and evolutions) Shark type
Held items related to Shark type
Mako Plate: Changes Arceus into a Shark type
Shark Memory: Same but for Silvally
Shark Gem: Boosts the power of a Shark type attack, but only once
Rough Scale: Boosts the power of the holder's Shark type moves by 20%
Other
Sharkium Z: Shark type Z crystal. Z Move is Great-White Rush
Max Jawstrike: Dynamax Move