I think you shall do freshwater fish or creature, sea is like DF fruit weak power

@Athena Shafiq depends on the fruit, Kaido can’t drown because he has a dragon/ fish fruit. Probably can swim in any water.

Nothing states he cant drown, the fish naming on the devil fruit is referred to as the scale similar to fish and in japanese folklore there a fish who evolve into dragon like magikarp turned into gyarados, it stems from chinese mythology where there is a koi fish who leaps waterfall called dragon gate and become dragon, all DF user weak to seawater thats the rule both in one piece universe and the tournament

Remember strawhat crew get to wano by giant koi fish that climb waterfall its referring to this legend, Zoan DF like lochness or crocodile might be possible but leviathan known for roaming the sea which contradicts DF

@Athena Shafiq get what your saying now.

Just make the devil fruit non-weak to its natural weakness? I mean its okay o break the main weakness of devil fruit users considering Blackbeard broke it by gaining two devil fruit powers.