Vistalancer's Cave (Patreon)

40 x 40 @ 150 pps

5th Level of Arkhan's Tower.

As he's a blue dragon it reflects its nature and natural habitat.
Have the PC run for DEX tests when moving in the icy floor. A fail means he fall prone and become an easy target for the dragon :p

Additionally you can use a numb mechanism that can slow and freeze the PCs if too much exposed to cold. The cave is a magic cold and is way more powerful than standard cold.
Your PCs can use fire spells, heat metal and other clever use of their magical items and spells to counter these effects such as a freezing fog, that can invade the level round after round, removing visibility and numbing the PCs. It would spice up the battle and allow Vistalancer to strike invisibly as he would be immune to the cold and the fog clouding. As a hunter he could try to strike isolated PCs one at a time, flying by, in and out of the cave using the holes in the tower.
He can also strike mounts of ice to make them fall on the PCs that are hiding or sheltering behind them.