Add some sort of visual on-screen when mutations like heart of ice, instinct of the master of arms, blind faith, etc reduce your skills cooldowns. I tend not to use these because I don't notice their effect hardly at all unless I'm using something with extremely large cooldowns like tonic, or a build designed specifically around spamming skills as much as possible. A visual effect would assist the player in knowing they should know to use their skill again soon.
I was thinking maybe something like a number value of the time reduced or a simple hourglass icon flashing by the player character when their cdr mutation is activated