View Solution

NOTE: You need to have unlocked the Darkasso for this achievement to pop

To get to -85% Cooldown you need:

- Both levels of the Cooldown PowerUp for -5%
- A fully upgraded Empty Tome for -40%
- Limit the number of active weapons to 1 and choose Arcana XX - Silent Old Sanctuary for another -40%

I recommend doing this achievement in Inlaid Library because it is an easy stage and has the Empty Tome as pickup, in case you don't get it as a normal choice.
You can quit out as soon as you reach -85%.