The upgrade cost for the elements skyrockets pretty fast in order to get to lv 20 it requires 333,782 of the required item for the upgrade. I'd like to suggest either hard capping the level height and manually setting the requirements, or allowing people to tweak it in the game settings.

On another note found one other thing with K2 spaced out. the ammo itself has a range limit, which is set to 30. When you have both range perks installed the range is increased to 55 but the bullet can only fly 30 so the turret sits there shooting at some thing in range but just cant hit it. This might have something to do with how K2 gives bullets weight and makes it so you need to manually aim.

Hello, thanks for the feedback.
I'll look into the ammo range issue and compatibility with K2 Spaced Out. If they implemented some sort of bullet weight logic, we might have a strong incompatibility that I might not be able to work around without breaking their intended balance.

For the upgrade cost, I wasn't sure which approach to take here, whether linear or exponential, or even capped.
When you suggest "hard capping the level height", do you mean capping the upgrade amount, but keeping it infinite (e.g: at lvl 20 and onward it always cost the same amount of material) or do you mean having a maximum rank for elemental upgrades?

In any case, making it tweakable in game settings is a good design philosophy which I'll aim to provide to players.

The K2 bullet weight issue should be addressed in the 0.10.3 release, let me know if it still is an issue during your play-through!

Hello,I really love this mod.But I don't know how to upgrade elements.I tried to click the element upgrade button when I got enough items in inventory, but seems not work.

Hello! Sorry it's a bit unclear I think, you are supposed to feed the items in the turret, just like ammo, in order to progress with the elements!

I don't find any slot or button can let me put upgrade items in. The button in the element window seems just show which item it needs. It doesn't work however I click it. And the progress bar can't interact.

Edited
Sorry, I got it now. You need to use the inserter not mouse click. Can't believe I am stuck in this for an hour XD.