Arctovish, the last of the Galarian fossils and by far the saddest. Not only is it's typing common, unlike the much rarer Dragon Electric, Water Dragon and Electric Ice typings, but does little for Arctovish offensively and defensively. Resisting only water and Ice isn't good, and the STAB combination is unremarkable as nearly every Water type gets Ice moves and a good chunk of the non Water Ice types get access to Water moves. Being walled by opposing Water types isn't a good footnote either.
Preferred Partners
Hail Setters -Snow Warning has great distribution so take your pick. Abomasnow, Vanilluxe, Aurorus, Alolan Ninetails all setup that sweet sweet hail that triggers Slush Rush and makes it possible for Arctovish to outspeed targets for Fishious Rend.
Grass types historically pair well with Water types, with both covering for each other's weaknesses. And this is true of Arctovish, though its lack of an actual Fire resistance hurts. Whimsicott probably makes for the best partner, also warding off Fighting types, providing speed control with Tail Wind and Stun Spore, etc.
Checks and Counters
The standard Water type counters work well against Arctovish. Ferrothorn can sit on Arctovish outside of hail and whittle it down. Rotom Wash easily resists both STABs and has super effective STAB of its own, as does Keldeo, but both must be wary of Freeze Dry. Regieleki can't come in safely, but if given a free switch, it naturally outspeeds Arctovish even with Slush Rush and easily OHKOs with STAB.