Because the sea weed

WORK IN PROGRESS.

Mareen
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Derivation: Corruption of Marine
Classification: Sea Sponge Pokemon
Abilities: Dry Skin, Swift Swim
Type: Water

No one knows what Mareen really look like. They sit on the sea bed concealed within sponges, allowing their long hair to flow freely in the water; since it is so long, however, they often end up getting things stuck in their tresses... including other Pokemon! Their hair grows rapidly, so even if it is torn or cut it will soon be just as long as it was before.

Mermareen
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Derivation: Mermaid + Mareen
Classification: Mermaid Pokemon
Abilities: Dry Skin, Swift Swim
Type: Water/fairy

Mermareen wrap their long and beautiful hair around their bodies to keep it from getting tangled and catching in things; they are very proud of their tresses and use their comb-like tails to keep it tidy and clean. They also have beautiful singing voices, which can cause sailors to dive into the water looking for them; this has unfortunately led to some deaths and the incorrect rumour that Mermareen do this on purpose.

Potential moves list: Sing, Attract, Perish song, Disarming Voice, Draining Kiss, Sweet Kiss, Play Rough, Fairy Wind, Moon Blast, Captivate, Disable, Echoed Voice, Flail, Round, Hyper Voice, Aqua Ring, Aqua Tail, Dive, Aqua Jet, Rain Dance, Water Gun, Bubble Beam, Vine Whip