During the mission in the Las Paridiso military base, Crypto says "Maybe we should have brought the Master Chief along."

Unlock the following skins by entering the corresponding codes at "Extras" > "Unlock Content". Then, select "Customize" at the options menu to activate the unlocked skins:

SKIN - HOW TO UNLOCK
60's skins (crypto) - M13Ni95L
70's skins (crypto) - S63bf2kd
Biker skins (crypto) - 1gb57M2x
Chef skins (crypto) - 51c24KiW
Gangster skins (crypto) - J5d99bPz
Kung fu skins (crypto) - Ly11r98H
Mime skins (crypto) - 7qd33J1n
Saucer attatchments - V81fvUW3
Saucer skins - X91mw7zp
Velvet skins (crypto) - F9sT5v88

Complete the game to get 3 million DNA and ammo recharge for your non-selected weapons.

Go to the space dust in Las Paradiso. If you look closely at the movie posters there is an ad for the original destroy all humans.

When transmographing objects, they usually disappear when transmographied. However, if you blow up a car and walk up to one of its wheels or tires and try to transmography it, you can do it for as long as desired. You can get every type of ammo. It will not stop until you release X. After releasing X, it will disappear.

Go to the Space Dust in Las Paradiso and look carefully at the movie posters to find an ad for the original Destroy All Humans!.

When you do the first story mission in Belleville, Pox will talk about video game ideas. Crypto will say "You're a plumber, but you don't use plumbing stuff to kill your enemies, you just jump on them", "You're a really fast hedgehog", and "You're a space marine on a planet with a ring around it". Pox will say that all of the ideas are crappy and then makes up his own idea.

In Belleville, the S.W.A.T. and the army will say ridiculous insults, such as "I fart in your general direction!" and "I wave my private parts at you, you son of a silly person!" These are insults from the movie Monty Python And The Holy Grail, in which the protagonists are taunted by French guards with these exact quotes and many others.

ACHIEVEMENT - HOW TO UNLOCK
High Roller (20 points) - Beat all story missions in Las Paradiso.
Destroy All Humans! (20 points) - Destroy 1,979 Humans.
A-Lister (20 points) - Beat all story missions in Sunnywood.
Zen Master (25 points) - Beat all story missions in Shen Long.
Big Fromage (30 points) - Beat all story missions in Belleville.
Furon Commander (35 points) - Beat all story missions on the 4th Ring of Furon.
Pox's Apprentice (20 points) - Beat half of the odd jobs in the game.
The Emperor's Agent (40 points) - Beat all odd jobs in the game.
Sacred Son of Arkvoodle (30 points) - Activate all landing zones all invasion sites.
Apocalypse Right Now (90 points) - Beat all Missions, Odd Jobs, Challenges, and unlock all Landing Zones.
Biologist (20 points) - Collect 10000 Furon DNA.
Biochemist (25 points) - Collect 1000000 Furon DNA.
Brain Surgeon (30 points) - Collect 5000000 Furon DNA.
Sleeps with the Fishes (20 points) - Destroy 15 Mobsters in Las Paradiso.
THQ 1138 (20 points) - Destroy 15 Lunarian Thugs in Sunnywood.
Fist of Furon (20 points) - Destroy 15 Triads in Shen Long.
The Francodyne Connection (25 points) - Destroy 15 Francodyne Guards.
Red Scare (35 points) - Destroy 25 Red Nexosporidium Warriors on the 4th Ring of Furon.
Massive Damage (20 points) - Trash 500 vehicles.
Paradiso Pursuer (20 points) - Find all the Furon Crash Test Dummies in Las Paradiso.
Sunnywood Seeker (20 points) - Find all the Furon Emperor Statues in Sunnywood.
Shen Long Scout (20 points) - Find all of Pox's Record Collection in Shen Long.
Belleville Beneficiary (20 points) - Find all the Furon Nails in Belleville.
Furon Factfinder (20 points) - Find all the Lava Lamps on the 4th Ring of Furon.
Fist Master (20 points) - Use the Temporal Fist 75 times.
Carnie (20 points) - Beat the Furon Librarian's high score in all of the Humania Games.
Shock Trooper (20 points) - Shock 100 humans with the Zap-O-Matic.
Proctologist (20 points) - Probe 100 humans with the Anal Probe.
Horticulturist (20 points) - Feed 100 humans to the Venus Human Trap.
Furoball Dribbler (20 points) - Bounce 100 humans with the Superballer.
Furon in the Sky (20 points) - Liquify 100 buildings with the Death Ray.
Flyswatter (20 points) - Take down 100 airborne enemies with the Seeker Drones.
DAHM Master (25 points) - Find all 8 DAHMs.
Pro-Pain (10 points) - Las Paradiso - Shoot a Propane tank cluster to blow up a building.
The 'Wood (10 points) - (Sunnywood)Destroy "SUNNY" on the Sunnywood sign.
Globeclotter (10 points) - (Sunnywood) Destroy several humans within 3 seconds with the globe.
Donut Holed (10 points) - (Sunnywood) Throw a civilian through the donut hole.
Definitely Not in Kansas (10 points) - (Shen Long) Use the Tornadotron to throw shipyard crates in the air.
Monkish Bowling (10 points) - (Shen Long) Use the bowling ball to bowl over at least 3 monks with a single throw.
Barge Boomer (10 points) - (Belleville) Destroy the barges.
Arc de Umph (10 points) - (Belleville) Throw a human above the Arc.
Crypto Sutra (90 points) - Beat all Paths of Enlightenment.