IOU

IOU is a consumable event item received from the Gambler (Gamblin) encounter. The item represents an "extremely legitimate" investment certificate and functions as a timed deposit that pays out a multiplier of the Gold originally invested when the Gambler returns to cash it in.

The Gambler can appear in the Forest, Castle, or Mines and may return after the initial encounter to redeem an IOU. When you receive an IOU you choose to invest either half your current Gold or your entire Gold amount. The effective payout multiplier depends on where you end up cashing the IOU in with the Gambler: the return increases by roughly 1.5× per area (rounded up). Concretely, cashing the IOU in the Forest returns 2× the invested amount, in the Castle returns 3×, and in the Mines returns 5×.

Use the IOU when your run benefits from a delayed large influx of Gold rather than immediate spending. Investing everything yields a larger absolute payout but carries the risk you will not encounter the Gambler again before the run ends; investing half gives a smaller payout but preserves some immediate buying power. Practical considerations:

• If you lack Gold for an imminent shop purchase or upgrade, avoid investing everything; invest half only if you still need immediate Gold.
• If the Gambler appears late (Mines or late in Castle), do not invest because the chance to meet him again is low.
• If you are actively farming events or deliberately exploring areas where the Gambler can reappear, investing (especially full investment) is worthwhile because of the high multipliers at later areas.
• Plan around area progression: cashing in earlier (Forest) yields modest returns, while waiting until Castle or Mines multiplies the payout substantially but requires surviving long enough to re-encounter the Gambler.

Flavor text on the item describes it as an exceedingly legitimate investment certificate.