I think what would be awesome is if, despite all their threats, large parts of the labs were just blocked by ice. And that ice contained within it stuff that was even worse.
Also, if we’re talking an active portal at the center to a cold realm, I can think of some good creatures to go with that, I think.
So what do we associate with cold - cutting cold, piercing cold, exhaustion, tiredness, numbing, pervasive, things solidifying, things sliding…
In the cold, everything is predatory. Life is hard, and you survive by killing others or by being so small they can’t be bothered to kill you…
Sylphs Sylphs are almost etheral beings, that make sounds in the air as they move reminiscent of wind chimes, and appear to be formed of complex patterns, shifting and moving and interlocking. They are creatures of the cold, creatures of a world utterly lacking in easy energy, and despite thier appearances are incredibly aggressive when not dormant. When still, they are almost invisible against the ice, and their clear bodies blend in well with most anything else too - but if disturbed, they strike. They will lock on to sources of heat, and close quickly, draining what heat the target possesses in a matter of seconds - their primary method of attack is the efficiency with which they can pull heat from their surroundings. They will also extinguish flames, gaining energy in the process, and will seek out warmer places, which they will make cold through their presence if the place is warmer than them. When enough energy has been collected and all immediate heat sources have been consumed, they will try to replicate, on the spot. The saving grace is their their adaptation to a cold world means that they will continue to feed, regardless of the costs, so long as energy is available - and it can not hold itself together under high amounts of energy. If it feeds on too much, too quickly, it will shatter. The limitless amounts of energy on the surface are effectively a death sentence.
Mechanics: Starts “dormant” and invisible. Wakes if player tries to enter square, moves next to square in any of the 8 directions, or starts a fire within a map tile. Special actions notes heat sources (including living creatures) on nearby tiles. Will reduce the heat on that tile, putting out any fires or “chilling” any creatures and gaining a portion of the “warmth” in return, assuming the tile is warmer than this creature. Has infravision. When it reaches enough energy, and there are no warmer targets, it creates a copy of itself and both are reduced to baseline temperature. If it reaches a certain warmth value, it will simply die and the heat will be released onto the square it’s on. Moves quickly, but not terribly durable. Attracted to fire and heat. Cannot bash down doors or windows.
Drops: “Shards” - these will break down in high heat, 80+ temp days, but can be used to make an incredibly sharp piercing weapon, “Sharp Spear”. (which will also break in 80+ temp days)