Gold looks like a side resource until a run stalls one card short of an engine. Then it is the only thing that can fix the draw. This guide is about earning it, spending it, and the Vault, the building most players skip and then wonder about.
Where gold comes from
Every king starts with the same income: 9 gold a year. Everything else is a card, a perk or a decree. The Vault adds 3 gold per level every year. Yield, a decree of the Jack of Rainbows, adds 9% of whatever you are holding each year, so it grows with the bank.
Greed's own cards fill in the gaps. Mortgage destroys a plot and pays 30 gold for each level it had, so a level 3 plot you no longer need is 90 gold. Spare Change is 9 gold when thrown into the pit. The Palace, Greed's base, makes golden enemies drop gold, and the Rainbow troop Scapegoat pays 3 gold a level when it is killed in battle.
What it buys
At the merchant, the first card costs 30 gold and each one after it in the same visit 15 more: 30, 45, 60. A reroll costs 10 and goes up by 10 each time. A new plot from the Expansion Tower is 30.
That makes rerolls the best value in the early merchants. The first two rerolls together cost the same as one card, and each one shows you a fresh store, which is how you find the one piece an engine is waiting on. The Bargain decree halves merchant prices and Outsourcing hands out 9 free rerolls, so a run that takes either can afford to search.
Why a Vault is worth a plot
A Vault does not need the King of Greed or any decree to pay. It levels itself every year, and at level 3 it pays 9 gold a year: as much again as your base income, from one plot and one card. Placed by the first merchant, that is nearly a reroll every year for the rest of the run, and a merchant card every few years.
It works for any king. The Vault is a Greed card, so other kings get it from the merchant or after beating Greed, and the earlier it lands the more years it has to pay. Even one bought at the year 19 merchant has fourteen years left to earn back its 30 gold several times over.
The value is in what the gold finds, not the gold itself. More gold means more rerolls and more cards at each merchant, and that is what turns a near-miss engine into a working one.
Where to put one
A Vault does nothing for the plots around it, so it belongs on the plot your engine cares least about. A corner is ideal: it has only two neighbours, and the plots with four sides are worth more under cards that buff what touches them.
Plan ahead if Chaos Earthworks is in the run. Then the Vaults go in a plus shape around one centre plot, with the Vault that will collect every level in the middle. Chaos Earthworks destroys whatever stands on those four sides, so keep any card you want to keep out of the shape.
Past level 3: Speculation, Earthworks and Chaos Earthworks
A Vault stops at level 3, and so does its income. Greed's decree Speculation lifts the cap to 99, for every Vault already on the board and every one placed later. Futurism does not: its 99 is for troops only, and a Vault is a building.
Earthworks multiplies Vaults. Played on a level 3 Vault it gives back 3 Vault cards and opens the plots around it. Set them down apart and each one starts levelling itself again, so one plot's income becomes three.
Chaos Earthworks goes the other way. It destroys the plots around its target and adds their levels to the target past any cap. Ring one Vault with others, play it on the middle one and the centre Vault takes every level at once. With Speculation, it then keeps levelling itself from there.
Cards that read your gold
Some cards turn the bank into strength, and they change how you spend. Mercenaries hold one unit for every 9 gold you have, so every coin spent shrinks the plot. A Dispenser gains 0.5% attack speed for each gold you earn, so it rewards income rather than savings. Over-invest goes the other way and spends 30 gold to add 15% to every stat of a plot.
Pick one direction for the run. A Mercenary kingdom wants gold kept, a Dispenser wants gold coming in, and Over-invest wants it spent. The Mercenary Bank build puts the first two together, with Vaults and Yield feeding both.
Mistakes to avoid
Leaving Vaults to the King of Greed. A Vault pays the same 3 gold a level whoever owns it.
Taking Futurism for the Vaults. It never lifts them. Speculation does.
Spending in a Mercenary run. Each 9 gold that leaves takes a Mercenary with it, rerolls included.
Saving gold past the last merchant in a run that ends at year 33. After year 31 there is little left to buy unless a card counts the gold.