Gold is the long game
Unlocks in the menu cost gold. The roster and the weapons both open through it, so a gold surplus speeds up everything else.
Farming is not exciting, but it is efficient. A few focused sessions clear the early unlock wall.
Pick a fast, repeatable stage
The best farming stage is one you already clear with time to spare. Speed matters more than a big single payout.
Shorter clears mean more runs per hour. More runs mean more gold, even if each one pays a little less.
Stack the bonus first
Check for any active gold bonus before you start. Turn it on, then farm while it lasts.
The gold and shops page explains where gold ends up once you bank it.