Kingdra

While Kingdra does stand out as the best Swift Swim attacker in SS DOU, it still leaves a lot to be desired. Its Speed in rain gives it a notable amount of utility, as it can pin down faster, frailer foes while it breaks the opposing team with strong rain-boosted Muddy Waters. In particular, Kingdra excels in using its offensive presence to give its teammates space and clean up weakened teams. However, it has multiple awkward matchups in the metagame, including against DOU's top threats in Rillaboom, Tapu Fini, and Kyurem-B, and its average Special Attack stat can at times feel lacking, which is a major downside, as it offers no utility outside of purely attacking. Kingdra, in particular, faces stiff competition as a Water-type attacker in rain from Urshifu-R, which boasts noticeably better power output and coverage, an improved matchup against Trick Room, more relevant utility in the ability to force trades with Unseen Fist, and most importantly a non-reliance on rain to be effective; while Kingdra does offer blazing Speed and a better match-up against fast Dragon-types in Dragapult and Naganadel, its Speed is also easily compensated for by the rain archetype's many Tailwind-setting Flying-type options in Tornadus and Zapdos, and its need for Speed also leaves it much more vulnerable in the face of opposing speed control. Kingdra's reliance on keeping its rain setter available, as it is very lacking as an attacker without it, on top of its other flaws, ultimately makes it quite awkward to run on rain teams.