This will show ya how to get the Skins for Destroy All Humans! (2020, Remake).
Original Skin (Crypto-137)
This is the Standard skin you start with.
The first objective for C-136 is easy, when you are in the base, just go around and start rapidly extracting some brains from random enemies. After you discover C-136 and blow up the lab, the game tells you to go to the saucer. DO NOT GO YET! An optional mission after this is required to get this skin. You must kill as many enemies until the mission is checked off.
In mission 7, after destroying all the buildings, leave at least one ice-cream truck alive. Go around and destroy anything military-related. (TANKS, Homing Missile Launchers, ETC) Once you react the limit you need continue to complete the mission.
Once you scan an explosive zombie cow’s brain, pick a cow up and find a scientist, throw that cow at the scientist. Once you reach the town hall meeting, scan 3-4 human minds there. Complete the mission.
At the start of this mission, You have to follow the car until it gets to the base, along the way you’ll find cables to bend. Bend all the cables it requires you to bend, do it before Armquist reaches the base otherwise they’ll disappear.
For this next one, while fighting Armquist, certain ammo will spawn around the base. Two spots are on the dock-ish area near the water. (They usually spawn late) There is also some more on top of the boat in the base there too, wherever the others may spawn I do not know, sorry.
From here on this is DLC skins, if you pre-ordered the game these should be unlocked for you.