The Fisher

The Fisher is a neutral mob that tends to spawn near water; like spiders, it is docile during the day, and may even be seen riding in a boat, fishing with its fishing rod. It fights by snagging you a fishing pole and dragging you towards it. Although not especially dangerous on its own, it can often prevent you from maneuvering while dealing with more salient threats. The Fisher will pull you constantly towards it at low speed, then suddenly jerking the line to pull you long distances. Dashing when they try to jerk the line will break it and deal the Fisher damage. Once it reels you in (gets you to within three blocks of it) it will begin to attack you with a melee attack.

There are four variant skin concepts for the mob. The idea was so broad I wasn't sure which one was the best fit for the concept.

The Fishing Spider
Drops: Spider Eye, String.  Probably my favorite skin option, because it adds value to the "Bane of Arthropods" enchantment and is also the cutest li'l guy. Look at him! D'aww, he's so cute.

Anglerfish
Drops: Prismarine Shard. Prismarine Crystal (very rare), Glowstone Powder (very rare). I liked the idea of an Anglerfish that drops glowing compounds.

Octopus
Drops: Ink sacs? Honestly I don't have a lot of ideas for super-valuable things for this guy to drop. If you do, let me know.

Angola
Drops: Bucket of milk, enchanted boots [depth strider], kitten [auto-named Fisher]. This is a really weird idea.

In theory, all variations may also drop: boats, enchanted fishing rods, or leashes.