Here is the full list of all 40 Destroy All Humans! achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Complete all optional mission objectives! (Use the Holopoxdeck if you have to.)
Ace all challenges!
Set something on fire, then use it to destroy a hapless human
Demonstrate Furon free spirit near a warning sign placed by the human authorities
Abduct and drain a vehicle to replenish your saucer's shields
Abduct a cow with your saucer
Display Furonic aeronautic prowess by soaring through giant human pastry without soiling your feet
Destroy humanity's last hope and initiate the subjugation of the species
Ace a Race challenge with a three-star rating
Destroy the pathetic human attempt at a robot overlord
Destroy a certain irritating simian warlord once and for all
Evade a rocket by dashing
Invade Capitol City
Invade Union Town
Invade Area 42
Obtain at least a two-star rating for each challenge type
Ace an Armageddon challenge with a three-star rating
Fully upgrade one of the branches of a weapon or ability
Accelerate Brain Extract or Transmog by mashing that button like you mean it
Use your saucer's Repulse-O-Tron to fend off homing missiles
Re-visit a mission in the mothership archive's Holopoxdeck
Transmogrify an object to replenish your ammunition
Invade Santa Modesta
Try out a new look for Crypto in the mothership's archives
Destroy multiple humans with a human-made explosive
Upgrade your saucer at Pox's Lab in the mothership
Ace an Abduction challenge with a three-star rating
Revisit a missionless invasion site and complete a challenge there
Ace a Rampage challenge with a three-star rating
Throw a human into the air and juggle them
Consume a human brain to kickstart your shield regeneration
Throw something into something else with the saucer's Abducto Beam
Stay covert by scanning primitive human thoughts
Invade Rockwell
Explore the more offbeat parts of the mothership
Upgrade Crypto at Pox's Lab in the mothership
Recover a Furon Probe
Use PK to destroy a human with another human
Destroy a human with a weapon and another with a psi ability at the same time
Invade Turnipseed Farm