Some of the enemies in the Heart of Ice Danger mission are invisible! When me and a friend started it after the first room then you head downward, the go left, there is a room with two freeze trapped framed with crystal and some breakable boxes. Behind them is a party button, when stepped on nothing happened, then my friend dropped dead. I tried to revive him but invisible enemies were blocking my way and I ended up dying. Another one of my friends has had this happened to him as well. I don't know if it's my computer's problem or the game's but please try fix it.