Currency
There are multiple currencies used in UnderMine.
Currencies are used for purchasing or unlocking items or familiars that help the player in accomplishing their task of finishing a run.
Gold
Gold is the most obvious currency used in the game.
Earning
Gold is collected from nuggets that around found commonly imbedded in the rocks throughout the game.
It can also be found
- in
Chests - from killing a boss for the first time
- using a potion called
Auglycerin
There are also multiple relics that can generate gold:
Lucky Nugget generates gold on a critical hit
Golden Popcorn has a chance of duplicating gold that falls on the ground
Bounty Contract makes random enemies drop gold if killed fast enough
Spending
Gold can be spent in a variety of shops available in the game.
Wayland, Arkanos, the Archmage and Dodson all have shops in the hub that allow you to purchase meta progression Upgrades, and Black Rabbit has a shop that allows you to spend gold to get a blueprint in the early game. Also the Red Shop Keeper has a store that will appear in the early game that allows you to purchase certain upgrades for Dibble's Emporium
There are also Shops that can be found through the game allowing you to purchase items, relics and potions with gold which include Dibble's Emporium and the Pilfer Shops mainly.
Finally there are a couple of miscellaneous tasks that involve using gold which include activating a lever to open a door in the Cavern Exit and Donating to the Tribute Fountain
Thorium
Thorium is a secondary currency, gained in small and rare quantities. The player is limited to a maximum of 999
Thorium at any given time.
Earning
You can earn Thorium from Thorium Chests damaging Hoarding Pilfer, by killing bosses in the Othermine, or by completing a run of Othermine.
Due to the fact that Thorium Chests and Hoarding Pilfer can be generated by potions, it can be said that Thorium can indirectly be generated by spending gold.
Spending
Thorium is mainly used for unlocking Relics, Potions, and Familiars
Its secondary use is purchasing 
Nether for 
75
Nether
Nether is a tertiary currency, it is extremely limited and not very useful, The player is limited to a maximum of 99 Nether.
Earning
Nether can be obtained at the end of your first complete Undermine run (The Gatekeeper gives you 3 on the ground), it can also be found at the end of an Othermine run (quantity of 1 in the chest), or gained by unlocking relics after completing your first run of Undermine.
Nether can also be purchased from The Gatekeeper at the cost of 75 Thorium.
Spending
Nether can only be used to pay The Gatekeeper to start an Othermine run.
Curse
Curses are an indirect currency in the game, and can simultaneously be considered an anti-currency.
Earning
There is a big incentive not to earn curses in the game due to their ability to increase difficulty.
Being an anti-currency the player earns curses in situations where normally they would be spending a currency, curses are mainly earned:
- Choosing a Legendary Relic at Sho'guul's lair
- Getting
Blessings at an 
Altar
They can also be earned through Hexes mainly
Siegfried's Torment a permanent curse is awarded every floor
Accursed items in Pilfer Shops cost gold and give two curses.
Spending
Curses typically spent in the traditional sense, rather reaching certain thresholds of number of curses tends to open a couple of opportunities.
- Sho'guul's lair can only be accessed by achieving the hidden curse threshold for the floor you are on.
Kurtz' Stache requires the player to get 10 curses after picking it up to do what it does.
The Familiar 
Lesser Demon gets paid in curses to increase its damage and laser size.
Being an anti-currency means that most players want get rid of the currency rather than accumulate it, however in WHIP curses are factored into the multiplier score so in order to maximize point players must maximize their curses.
Bombs and Keys
Bombs and Keys would not normally be considered currency, however Black Rabbit's shop accepts them as payment such they are considered currency.
The player can only hold 99 bombs and keys respectively.
Earning
These items can be purchased at shops for gold or found in Chests and Containers throughout the run.
They can also be gained by drinking potions
Potion of Plenty gives a key and a bomb
Doubling Saison doubles the players bombs
Blood Chalice gives a bomb or key or bomb bag or key ring at the cost of health
Iron Glaze can sometimes generate a bomb or key due to rounding
Impish Key Bomb converts bombs to keys and keys to bombs.
Spending
Keys can be spent to gain access to certain rooms with locked door
Bombs can be used to open secret rooms, crawlspaces, and certain shops which are only accessible by bombing Walls.
Bombs and Keys can be spent at Black Rabbit's shop for items and relics.
Health
Health under certain conditions in the game becomes a currency that is used in the place of gold.
Earning
Every run is started at full Max Health, this amount is determined by the number of tunic Upgrades the player has.
When the player spends health they can regain it by eating Food or drinking Potions. 
Sol's Phoenix will also give the player back some health when they lose it.
Spending
The main way to spend health is with the curse 
Blood Offering which converts gold costs in shops to health costs, however an alternate way of spending health is through the curse 
Bloodied Locks which forces you to spend health to get through locked doors instead of keys
Health can be wasted by getting damaged from not dodging attacks.
Most health costs cannot be bypassed by 
Armor Shards
Obsidian Knife is lost when spending any health (but not when spending Max Health which can be done with 
Soul Guard)