PUFFERFISH

Nothing else in the game drops a pufferfish. Not a mob it lives alongside, not a chest, not a loot table shared with any other item, only the fish itself, caught on a line or killed outright, one puff at a time. Eating it raw poisons you, so most of what gets caught ends up as a brewing ingredient for water breathing rather than food, and the surplus is what a Fisherman is willing to buy.

He is also slow to offer it. Master sits at the very top of his ladder, the last tier a villager reaches, so this is not a trade you stumble into early.

To sell pufferfish for emeralds, bring it to a Fisherman at the Master tier, 4 units per emerald.

The best rate any villager offers is an emerald per 4 pufferfish, from the Fisherman, and 5 of the other 10 pay out faster. No villager sells pufferfish back, so it is emeralds out and nothing in.

One slot at the Fisherman takes 4 pufferfish a trade, 12 trades, 12 emeralds. 8 of the 72 villagers that pay emeralds, emptied out:

12 acacia boats against 312 flint for the same 12 emeralds, 26 times the carrying, and the shortest wait is the Butcher at 7.5 real minutes of shelf, gathering not counted. Pufferfish itself pays 4 an emerald, so 13 of the 72 ask less and 50 ask more.

Every pufferfish offer here locks after 12 uses, and a villager restocks up to twice a Minecraft day, no more.

The earliest pufferfish shows up is the Fisherman's Master tier, level 5 of five, the top of the ladder. A freshly employed Fisherman has climbed nowhere near it.

12 trades empty the slot, and 2 real minutes later it refills, the same clock every Fisherman shares. A Minecraft day holds two of those refills across 20 real minutes.

One Fisherman worked through both moves 96 pufferfish for 24 emeralds, a modest total against how long a Master tier takes to reach in the first place.

One villager, one restock: the Fisherman pays an emerald per 4 pufferfish and that slot runs 12 trades, so 48 pufferfish is all one will take before it locks.

Where they go back: campfires are that Fisherman's cheapest offer.

Also on the Fisherman's list: oak boat, spruce boat, jungle boat, acacia boat, dark oak boat and string.

Eating a pufferfish is a mistake: it poisons, nauseates and drains hunger. Its value is entirely in brewing, where it is the ingredient for Potion of Water Breathing, the potion that makes an ocean monument or a long underwater build possible at all.

Fishing is the usual source and the fish is one of the junk results, so a rod pulls them up without being aimed at them. The bucket version keeps the fish alive, which is how one ends up in an aquarium rather than a brewing stand.

The potion is a nether wart base with a pufferfish added, and redstone extends it. There is no stronger version, because there is no such thing as breathing harder, so redstone is the only upgrade that applies.

Where it earns its place is an ocean monument. The guardians, the elder guardian's mining fatigue and the sheer distance between air pockets make a monument the one build in the game that punishes you for surfacing.

A conduit does the same job permanently once you have eight nautilus shells and a heart of the sea, which is why water breathing is an early answer and a conduit is the late one.

A Pufferfish turns up often enough on a fishing rod that an AFK fish farm keeps the Master Fisherman supplied: he takes 4 Pufferfish per emerald, 12 times over. How to Build an AFK Fish Farm in Minecraft covers the build.