The Abyssal Scyphoid is the glowing jellyfish of the Ice Maze, a water creature that spawns in small groups near the surface and never moves from where it appeared. It has no attack and it doesn’t chase, but touching one, or hitting one up close, gives you Poison III and Blindness for 3 seconds each, and it keeps giving them for as long as you’re in contact.
Its health depends on its size, from 4 on the smallest to 28 on the largest, and it drops 
Jellyfish Jelly, which is the food that grows a Scuttler into a Shellback. This page covers where they sit, exactly what contact does, how to kill one without being stung, and what’s worth collecting from it.
Spawning
Abyssal Scyphoids spawn in the water of the Ice Maze as water ambient life, the same category as the 
Spinefish and vanilla fish, which means they’re common and they ignore light level entirely. In the Overworld they come in groups of 2 to 4 and use the surface rule, so they’re found within about 13 blocks of sea level rather than down on the floor.
Each one rolls a size when it spawns, from a quarter of the normal model to nearly twice it, and its health is set from that size at 16 per unit, which gives the range of 4 to 28. A big one is noticeably bigger and considerably harder to kill. The Maelstrom spawns them in fixed groups of 4.
Because they’re animals rather than monsters they spawn on Peaceful too, which makes the Scyphoid the one thing in the maze that can still hurt you with the mobs turned off. It can’t kill you on its own, as Poison stops at half a heart, but Blindness underwater has other ways of doing that.
Behavior
A Scyphoid has no movement code at all. It hangs where it spawned, pulsing with a squelch that comes faster on the small ones and slower on the big ones, and it never turns toward you or follows. Whatever water it spawned in is the water it stays in, which is why a cluster is more like a minefield than a school.
Contact Poison
Anything that bumps into a Scyphoid gets Poison III and Blindness, both for 3 seconds, and the timers reset every moment the contact continues. Hitting one in melee does the same to whoever struck it, as it stings back the instant it takes damage. The two things it won’t sting are another Scyphoid and the Anglerfish, which is why the fish can hunt through a cluster that would blind you.
Ranged attacks are safe. The sting on being hit goes to whatever touched it directly, so an 
Arrow or a thrown 
Trident takes the sting and you don’t, which is the whole basis of dealing with them. Creative and Spectator players are skipped too, if you’re placing them for a build.
Poison III can’t take you below half a heart, so the Scyphoid’s poison never kills on its own. The Blindness does the killing, by blacking out the water while a Maw is closing or while you’re 20 blocks from air, and it refreshes for as long as you’re touching the jellyfish. Get clear first, then worry about the poison.
Out of the water a Scyphoid dies instantly. Any tick it isn’t in water or a Bubble Column it takes 1,000 damage, which means one that gets pushed onto the ice or drained by a 
Sponge simply vanishes. There’s no carrying one home, and no Bucket for it either.
Drops
A Scyphoid killed by a player rolls 0 or 1 times on a pool that’s half Jellyfish Jelly and half nothing, which works out to a Jelly from about 1 kill in 4, and each level of Looting adds up to 1 more Jelly to a kill that drops one. One killed by the Shipbreaker’s head drops a 
Ship Graveyard Echo every time instead, and that’s the only way a Scyphoid gives one.
Abyssal Scyphoid Drops
Jellyfish Jelly 
Jellyfish Jelly is a poor food and a good ingredient. Eaten, it restores 1 hunger with a high saturation and carries a 10% chance of 3 seconds of Poison III, which is the jellyfish’s revenge. Fed to a Scuttler it adds a quarter to the crab’s size each time until it turns into a Shellback, which takes 9 to 13 pieces depending on how big the Scuttler started.
It also goes into the 
Poseidon Breakfast, the strongest meal in the mod, alongside 
Cooked Spinefish, an 
Esca and a 
Void Squid, though on 7.1 that recipe can’t be finished, as Cooked Spinefish has no way to be made. Given the 1 in 4 rate, a Shellback costs somewhere around 40 to 50 Scyphoid kills without Looting, so the sword you bring to a jellyfish field matters more than it looks.
Frequently Asked Questions
No, it has no attack and can’t move, so it never comes to you. The danger is contact. Touching one or hitting it in melee gives Poison III and Blindness for 3 seconds each, refreshed for as long as you stay in contact, and it spawns on every difficulty including Peaceful.
From range. The sting goes to whatever hits it directly, so an Arrow, a 
Crossbow bolt or a thrown Trident takes it instead of you. It can’t move, which means you can shoot a whole group from the ice, and a 
Bow kill still counts as yours for the Jellyfish Jelly drop.
Jellyfish Jelly from about 1 player kill in 4, with Looting adding to the count when it drops, and a Ship Graveyard Echo every time the Shipbreaker kills one. The Jelly is the food that grows a Scuttler into a Shellback and an ingredient in the Poseidon Breakfast, and it’s a weak snack on its own with a 10% chance of poisoning you.
Between 4 and 28, set by its size at 16 health per unit of scale, with the scale rolled between a quarter and one and three quarters when it spawns. It also takes only 20% damage from weapons without Depth’s Fury, so a large one takes around 20 hits from a plain 
Diamond Sword.
