Heart of Ice is a Survival-scaling mutation which lowers the cooldown of skills when attacking enemies which are stunned, rooted, slowed[a] or frozen at close range.
Attacking a frozen, slowed, stunned or rooted enemy at close range will reduce skills cooldown by [0.6 base] seconds.
Scaling: +0.105 seconds per Survival stat
Number of stats
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15+
...
Mutation effect
0.6s
0.705s
0.81s
0.915s
1.02s
1.125s
1.23s
1.335s
1.44s
1.545s
1.65s
1.755s
1.86s
1.965s
2s
...
Notes
The effect has a 0.5 seconds cooldown.
Phaser is extremely powerful with this mutation, as it essentially allows for infinite use of the item.
It is also very effective with items that rely on rooting/stunning/freezing for critical hits, such as the Nutcracker or the Repeater Crossbow, as it can allow for rapid skill cooldown reduction and open up many powerful combat options.
This mutation pairs well with Melee and a fast swing rate melee weapon like Cursed Sword because you are constantly hitting a slowed target.
Footnotes
↑In-game description is incorrect. Although it doesn't say it, this mutation works on slowed targets as well.
Phaser is extremely powerful with this mutation, as it essentially allows for infinite use of the item.
Nutcracker or the 
