Not to be confused with Frost Relic from Risk of Rain.
The Frost Relic is a returning item in Risk of Rain 2, having gone from Uncommon to Rare. It surrounds the player with a circle of damaging icicles when they kill an enemy.
Since the area moves with the player and is relatively small, this item is most effective with the melee-focused Mercenary and a ramming MUL-T. Other classes tend to try and stay away from enemies, but flame-spewing Artificers make good use of this as well.
As with most items, the Engineer's Auto-Turret will inherit this item and surround themselves with icicles.
The Huntress may want to pass this pickup to a more suitable friend, as her ranged abilities and fragile nature encourage her to keep her distance from enemies.
In-game screenshot.