Drowned with tridents can have them be changed into fishing rods when attacking a target and still shoot tridents. A nautilus shell can also be suddenly in their offhand after attacking a target.

Steps to reproduce

1. Open MCPE-40288.mcworld . This word contains a trapped villager, a short minecart track, and a saved drowned-with-trident-in-minecart structure.
2. Flip the lever. This will load a drowned with a trident in a minecart and start sending it back-and-forth along the track.

Expected result

The drowned with the trident keeps the same equipment.

Observed result

If you wait long enough the drowned will eventually acquire both a fishing rod and a nautilus shell.

Analysis

This is a bug in the vanilla behavior file. Every time a ranged drowned switches to melee mode because its target is close it also loads the melee equipment table, which gives it a chance of getting fishing rod and nautilus shell. To fix the bug, move the melee equipment table to its own component group that would be added only when spawning a melee drowned. (This bug and the fix needed is analogous to MCPE-137149; compare zombies who have a separate component group for spawned equipment.)

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Ok, so I was randomly messing around in my world when I suddenly noticed that after a drowned with a trident threw it at a villager and killed it, the drowned suddenly had a fishing rod. Hours later, I was testing to see what was the issue and another drowned with a trident suddenly had a nautilus shell in its offhand. After spawning loads of villagers, its trident became a fishing rod and another bug was discovered: it could still shoot tridents even though it had been replaced by a rod. This is confusing but if I had to guess, the chance of the drowned's trident of changing into a rod (and the drowned to suddenly have a nautilus shell in its offhand) are the same as the chance of finding a drowned with the item. The video I recorded was too long to upload but you could try to test it by:

1. Spawning a drowned with a trident in a river or ocean in Creative Mode with Easy difficulty (so no zombie villagers), and clearing other drowned from the area.
2. Spawn one villager at a time in the same river/ocean as the drowned, but at a distance such that the drowned wants to use its trident instead of melee.
3. Let the drowned kill the villager and repeat, until its trident turns into a rod. This may take a while. Also, a nautilus shell may also suddenly appear in its offhand.
4. Once the trident turns into a rod, test whether the drowned can still shoot tridents, using villagers. Note that the drowned can drop the rod like normal.

Is there a way to send the video to anybody so I can show more proof?