Gold

'''Q: What do I use gold for? / Do I only use gold to level up monsters?'''

You only use gold to upgrade monsters in your current run. I know it sounds useless or simple, but you'll find out gold is a major limiting factor when it comes to progressing. There isn't a big need to worry about it early on, but you will have to keep an eye on it if you're ever stuck or looking to progress.

Q: I'm wave XX, is it normal for monsters to keep dropping 1 gold?

Actually, yes. Unlike most other idle games where stronger monsters drop more gold, in this game most monsters (not all, as there some exceptions) only drop 1 gold until you upgrade gold drop.

Q: How do I increase Gold Drop?

There are multiple ways: if you want to upgrade flat gold drops values, there are upgrades for that in every upgrade tab besides Spells (one of which can increase gold drop by a % temporarily). You can also increase a monster's alchemy attribute level to increase gold drop by a flat value, but you take benefit from these levels only if the monster with the alchemy levels kills an enemy.

To increase gold drop multipliers (or chance multipliers), you can check the following upgrade tabs: Spells, Relics, Tech Tree, and Tournament Upgrades.