not sure if intended but buying upgrades requires you to have money equal to original price even when you have rebirth discounts (although the actual money spent is discounted).
If you use clouds with absorb, you can have a 300+ turn "powerful" buff with numbers that are too large to even fit in the screen. I think it's overly exploitable and sort of breaks the game, as you can one-shot all enemies even with a very low flux cost (even 1 flux). and have heals that always restores you to full health (also possible with 1 flux). The only catch is that you can die by stepping on your own cloud, which I found a bit frustrating. I think there should at least be an option to warn the player of potential damage when moving into a tile.
I think firing speed of 9 on the watcher is a little overnerfing it... or maybe nerfing the kills to damage instead of the firing speed might be better because now its just too slow.