This magical created boss room hides a beast, which is perfectly adapted to all regions contained here. It has its own strengths in each area:
Snow: The beast's sweat freezes on its body and forms a hard protective layer.
Jungle: The beast is well camouflaged in this area, attacks and then immediately disappears into the undergrowth
Lava: The beast is covered in the liquid rock and each attack causes additional fire damage
Water: It can swim excellent and breathe underwater. Although the advantage contained here is not too great, it is offset by the fact that our heroes probably performe worse in water than on land.
I would suggest to create some kind of compulsion that forces the beast or heroes to move from one area to the next again and again, so that the fight becomes exciting and varied.