Destroy All Humans! - Clone Carnage

Here are the two stages I used for this achievement.

Rampage - Rockwell "Rockwell BBQ"

This one is very easy, I personally did it solo with a second controller idle, in terms of upgrades I suggest using Gortan Shock Multiplier, Compound-R-Izer, Proton Protonizer and Ion Votex Coils. Follow the drone with the cow hologram around and keep killing, you should have plenty of time to 3 star this without much difficulty at all.

Abduction - Turnipseed Farm "Cornered Beef"

This one is extremely difficult and extremely luck based. Personally, I couldn't get this one solo, and had to do it co-op. I did manage to score 176 points solo, so it *might* be doable, but I suggest saving the stress and doing it with a second person if you have anyone around locally to help.

The only upgrade I found which may help is infinite skate. The important thing for this mission is to keep moving keep moving, and keep delivering. If you're going solo, focus on the green radioactive cows when possible, but ensure that you're not abandoning the giant groups of regular cows as they can be worth a decent amount of points too. If you're playing two player, one player should follow the beam and clear out the groups of cows, while the other player splits off and looks for radioactive cows. The cow spawns are random, so make sure to constantly keep an eye out and keep checking areas, even if you've checked them before.

Make sure you are aiming high when throwing to ensure that the cows aren't hitting anything and dying before reaching the beam. This is especially true for the Radioactive cows, who blow up on contact with anything, resulting in no points. It may be better to spent a split second longer to line up a shot perfectly, than a risky shot that ends with less points. Luckily the hitbox for the beam is wider than the beam itself, so while you do have to be accurate, you have a slight margin for error.

If you see the agent, grab them for a large amount of points, however you don't have a lot of time to spare, so unless they happen to spawn in a lucky location, it may not be worth the time to it would take to find them otherwise as the spawn is random.

Good luck, this appears to be the hardest achievement in the game, so if you can unlock this, you should be good for the completion.