Oh please add a "buy max" or "buy 10" option (e.g. shift+click buys max possible). My mouse is breaking! ;)
Caiburn
Recent community posts
A tiny probably super rare bug: Skulls can get pushed outside the left border of the arena where they then drift slowly to the left ("under" the upgrade buttons) and don't do anything until the arena ends. I guess it only happens when they attach to a mob on the extreme left side of the hitbox and then the mob gets pushed into the left border.
How about a real achievement system (aside from skins)?
Something like "Achievement: Electrician (Do 1/10/100 million damage with Chain Zapping)" // "Achievement: Ninja (Get 100 killshots with daggers)" // "Achievment: I have seen that before (re-run the same arena 20 times without a rebirth)"
Could add a "x2 income every 22 achievements" mechanic.
You have a ton of possibilities here to channel your creativity into, and should you ever get it to a state where you can realistically put this on Steam you'd already have a tie-in to that achievement system ;)
Speeding up progression a bit is surely a good idea. If you look at the price increases between upgrades especially at the higher end it becomes disheartening (e.g. Master Wiz->Zap Dmg).
The question is what you want - should the player be more looking to upgrade the current "life" (then lower the costs a bunch) or rather rebirth often and upgrade the whole run (which seems to be the standard with games that have a rebirth mechanic)?
You are the god of the game, you make the rules :) I'm sure you've played a fair share of idlers before deciding creating one...so look at what made those games fun and take inspiration from that - if you want. :)