Overflow Points

Overflow Points are the reward for completing Overflow Challenge

You can use overflow points to buy various perks:

The cost for the next level is (base cost)*(num bought + 1)

Because of the cost increase, it's generally hard to spend all your points in one area and better to mostly spread them around (aside from regen, which is useless). Buying more levels of BH is very helpful in 1CCC. Going heavier on CP, CS, and CC when available is generally a good plan.