There are three Lurker Glacial Troops scattered around Snowy Mountain. They will come out of battering rams, and will shoot at you and hold shields. You cannot damage them unless you have red eco. Luckily, there is a red eco vent near all 3 Troops. Get red and break their shield with a basic attack, then simply kill them.
The first is at the top of the hill that the snow boulders roll down. At the top, turn left and defeat all the enemies you find there.
The second is just past the pond near the entrance to Snowy Mountain.
The last group can only be accessed after you have opened the Lurker Gate. Once you have, jump onto the platform. At the upper level, head right to find the last group.