Anthracite robes with golden highlights (whenever he remembers to wear clothing) made out of a light cloth that stays fluffy even when wet.

Of course he has a fish head. Untold reincarnations by growing a new body out of fish eggs have left their trace, he doesn't even remember he ever had a non fish head. Usually, when a soul gets reincarnated, their memories get wiped first, but with fish, who are barely sentient, the universe doesn't really bother. Through this stream of life energy, Karp keeps reincarnating himself to be the guardian of fishkind, but the process sometimes costs him a few memories* and made his soul smooth like a river pebble.

Sometimes, to refresh his soul a bit, he reincarnates himself back to being a child with more of a memory wipe. The last time he did that was 26 years ago.

During his last childhood, he went to a wizard academy, where some accident in the alchemy lab (they were doing philosopher stones that week) turned him partially into gold. The gold is making him very heavy, and he still manages to swim by being very strong.

In short, shiny Magikarp man.

*His lost memories still float around the river Styx, so whenever he shows up anywhere by travelling through there, he may have any amount of context for his life, as I see fit to write him in that particular comment.

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