Honestly the whole "Dendy is a kappa" thing bugs me. Because Dendy is basically drawn exactly like everyone else. Dendy doesn't have any water-y features or a turtle shell or anything (at first I thought "oh, maybe her backpack is like her shell" but that was disproven pretty fast)
She doesn't have a divit with water in it. She doesn't have a beak (unless you count that cute little "v" mouth she has as a beak). Basically her design makes absolutely no effort to look even remotely kappa like. Then I thought "oh maybe she's just half-kappa and takes more after her human parent". But we see both her parents and they're both kappa. Not only that but they both have green skin and divits in their heads full of water like traditional kappa.
I dunno, why make her a kappa at all if she's only going to be one in name?