The bestiary entry can be obtained by reading Of Fire and Stone, which however (while existing in the base game files) cannot be obtained before the Blood and Wine expansion.
Bestiary entry[]
I thought to myself - what's a hunk of ice doing in the middle of some lab? And then that hunk of ice got up and broke my legs. – Yannick Lovt, burglar
An ice elemental is a mass of frozen water animated by magic. Deprived of consciousness or independent will, this elemental is boundlessly obedient to the orders of the mage who created it. Those orders usually contain but one syllable: kill.
Ice elementals have no qualms about carrying out this order nor any particular difficulty in doing so. Gifted with incredible strength, they are completely invulnerable to poison and fire, deprived of sensitive organs, hard as permafrost and all in all incredibly difficult opponents. A witcher's only chance at tipping the scales towards victory is to toss a dimeritium bomb – shrapnel made of this metal interferes with the workings of the spell that gives this creature life. Beyond that remains only prayer.
Combat tactics[]
Ice elementals fight similarly to earth elementals. They can strike with their massive fists, stomp on the ground to knock over their targets, or send a ripple of ice carving through the terrain at their foes. As with other elementals, avoid attacking the elemental from the front if you can, dodge its attacks as they cannot be parried, and make extensive use of Yrden to slow it down.