in the freezer you get 2 items that are needed the waste disposal card key and the infrared scope it allows you to see invisible los plagas on the regeneraters. equip the infrared scope to the 223 caliber rifle and aim at the regeneraters. p.s. there is a even harder regenerater that gets near you and etracts spikes and does serious damage he also has 1 more los plagas on his back just shoot his leg/foot than shoot the one on his back ( make sure to have lots of rifle rounds)
good luck

you must get the infared scope in the freezer room