Gold Worm

The sell price is large and that is the trap. Shimmer converts it into a Gummy Worm, which is a permanent lift to your fishing power for the rest of the run. Coins are replaceable and that is not, so unless you already have the buff, the shimmer pool is where this belongs.

Bait power is high and the chance of it being eaten is far below anything else in its class, so one of these lasts several times longer than an equivalent golden critter. The Tackle Box does nothing for it, which hardly matters given it was already the most economical bait in the game.

They replace ordinary worms occasionally, so the same rainstorm that gives you a pile of regular ones is also your best shot at a gold one. A Lifeform Analyzer calls them out when they are nearby, which is the difference between hunting for one and stumbling onto one. A Can Of Worms is the other route, at far better odds than the wild spawn.