1) Urn, that green gas occupies too much space, also some transparency should be added (great design btw)
2) Medalion's features are unclear, should make it less "golden", its too clean
3) threads and HoD are glossy, remove it
4) remove background gradient from Eul
5) remove background gradient from Butterfly
6) remove background gradient from S&Y
7) remove background gradient from BoT
8) remove background gradient from Drum
9) remove background gradient from headress
10) remove background gradient from armlet
11) remove background gradient from veil
12) remove background gradient from dominator
13) remove background gradient from Rod of athos
14) remove background gradient from blink
15) remove background gradient from Ultimate Orb

When I say remove, I mean, add proper transparency, to preserve contrast and have a general design direction.

The only items that should have a backgorund gradient are the toggled items (armlet, basilus, radiance. aquila)

As a design improvement for the future, you could create a new Icon state for the activable items as well, to be shown while the cooldown runs out. There could be like a gif, transforming back to the initial state.