The Terrible and Abyssal upgrades are the two 
Smithing Table recipes that turn Iron Armor and Diamond Armor into Aquamirae’s own armor sets, and they work the same way a Netherite Upgrade does. The 
Terrible Upgrade takes Iron Armor and a 
Fin, the 
Abyssal Upgrade takes Diamond Armor and an 
Abyssal Amethyst, and both templates are consumed with each piece.
What you get out of it is armor that actually holds up against the Ice Maze creatures, which ignore most of what normal armor does. This page goes through the forging itself, what the finished pieces are actually worth, and the order you’ll want to do it all in, while the Smithing Templates page goes into more depth on finding and duplicating the templates themselves.
Getting Started
Everything starts with a Terrible Upgrade Smithing Template, and the only place they come from is a 
Pirate Pouch or a 
Treasure Pouch, each with a 10% chance of holding one.
Once you have a single template you can duplicate it at a 
Crafting Table with 4 Fins and 4 
Angler Fangs, which gives you 2 back, and that’s how you turn one lucky drop into a full set’s worth.
2With a few templates banked, take your Iron Armor to a Smithing Table piece by piece with a Fin for each. Fins are the most common drop in the biome, coming off Maws, Anglerfish and Eels and out of Pirate Pouches, which means the templates are the real limit rather than the material.
The finished Terrible set is a real step up from Iron without needing a single 
Diamond. It comes to 17 armor points where Iron only has 15, it has no toughness, and each piece will last around 3 times as long as the Iron piece it came from, with the 
Chestplate alone holding 750 durability.
It repairs on an 
Anvil with Angler Fangs or 
Ship Graveyard Echoes, and it enchants the same way Iron does. Either of those materials is easy enough to come by that keeping the set in good shape is never a problem.
The Two Upgrade Tiers
Terrible is the mid game tier and Abyssal is the end of the line. Abyssal starts from Diamond rather than Iron, which means it keeps Diamond’s 20 armor points and its 2 toughness, it adds more Resilience per piece, it lasts more than twice as long as Diamond does, and it glows faintly in the dark as well, which is a nice touch when you’re down in a Pirate Shelter.
Terrible Armor
Abyssal Armor
Forging Abyssal is the same three slot job with a Diamond piece and an Abyssal Amethyst, and the difference is entirely in the template.
The Abyssal Upgrade Smithing Template never drops from anything and can’t be duplicated, as it’s crafted one at a time from a Terrible template surrounded by 4 Abyssal Amethyst and 4 Ship Graveyard Echo, with the Terrible template consumed in the process.
Note that the 
Abyssal Tiara isn’t part of this. It’s the set’s second helmet and it’s crafted straight from a 
Totem of Undying and 4 Abyssal Amethyst with no template involved, which makes it the one Abyssal piece you can make before you’ve done any smithing at all. The 
Abyssal Heaume is the helmet that comes off the Smithing Table.
Progression
The whole chain runs from one looted template to a glowing Abyssal set, and each step feeds the next. The Abyssal end of it is deliberately expensive, which is why it pays to gather the amethyst and Echoes before you convert any templates.
Find a Terrible template
Pirate Pouches and Treasure Pouches, 10% each
Open every Pirate Pouch you come across until one turns up. You only need one, as the duplication recipe takes it from there, but don’t spend that first one on a piece of armor until you’ve made copies of it.
Forge your Terrible set
Iron Armor, a template and a Fin per piece
2Duplicate up to at least 4 templates, then run each Iron piece through the Smithing Table with a Fin. Keep going past 4 if you can, as every Abyssal template you make later will cost a Terrible one.
Craft the Abyssal templates
A Terrible template plus 4 Abyssal Amethyst and 4 Ship Graveyard Echo each
Abyssal Amethyst comes from the Maze Mother and occasionally a Treasure Pouch, and Ship Graveyard Echoes only drop from creatures the Shipbreaker kills, which makes this the slow part. Each template you craft here is one Abyssal piece.
Forge your Abyssal set
Diamond Armor, an Abyssal template and an Abyssal Amethyst per piece
Craft a piece from four Diamond pieces, four 
Abyssal Templates and four more Abyssal Amethyst at the Smithing Table. If you’d rather have the Tiara than the Heaume, you can skip the helmet here and craft the Tiara instead.
Adding it all up, a full 4 piece Abyssal set costs 4 Terrible templates, 20 Abyssal Amethyst and 16 Ship Graveyard Echo, and the checklist below is the shopping list for it. Sixteen of the crystals and all of the Echoes go into templates that get destroyed, with the last 4 crystals spent at the table itself.
If you go with the Tiara instead of the Heaume, knock one Terrible template, 4 Abyssal Amethyst and 4 Echo off that list, and add a Totem of Undying and 4 Abyssal Amethyst for the Tiara itself, which comes out slightly cheaper overall. The Tiara route also skips one trip through the Smithing Table, which matters more if you’re short on Echoes than on crystals.
Tips
Enchant the base piece before you forge it if you like, as everything on it carries across, but there’s no penalty for doing it afterwards either. Terrible enchants like Iron and Abyssal enchants like Diamond, which means the 
Enchanting Table treats them exactly as it did the piece they came from.
Don’t rush past Terrible to get to Abyssal. A full Terrible set already turns the Ice Maze creatures from lethal to manageable, and it costs 4 Fins and 4 templates, while a full Abyssal set costs 16 Echoes that you can only get by waiting on the Shipbreaker.
Treat the Terrible templates as the currency of the whole system and keep duplicating them whenever you have the Fangs. Every armor piece eats one and every Abyssal template eats another, and running out halfway through a set means going back to opening pouches at 10% a time.
Match the armor with a weapon from the same family before you fight anything serious. The armor stops you dying, but a 
Terrible Blade or a 
Shatterblade is what makes your hits land for more than a fifth of their damage, and it counts as a piece of the set on top.
FAQ
The mod’s own creatures, which is the Maw, Anglerfish, Eel, 
Spinefish, Abyssal Scyphoid, Shellback, Tortured Soul, Maze Mother and the Ghost of Captain Cornelia. Against those, the Depth’s Resilience on each piece brings back the armor value they’d otherwise ignore and cuts down the triple damage criticals they land. Against ordinary mobs it’s just tough Iron or Diamond.
The Terrible Upgrade Smithing Template drops from Pirate Pouches and Treasure Pouches at 10% each, and once you have one you can duplicate it with 4 Fins and 4 Angler Fangs. The Abyssal one is never found, only crafted, from a Terrible template plus 4 Abyssal Amethyst and 4 Ship Graveyard Echo.
Yes, every time. One template makes one piece of armor, which means a full set needs 4 of them, and since the Abyssal template can’t be duplicated a full Abyssal set is the most expensive thing to build in the mod. Duplicate your Terrible templates early so you never run short.
On the numbers, yes, as it keeps Diamond’s armor and toughness, adds more Resilience, lasts longer and glows. Terrible is the better value though, as it costs a fraction as much and already fixes most of what makes the Ice Maze creatures dangerous. Build Terrible first and move to Abyssal once the Echoes are in.
