Here is the full list of all 30 What's the Matter? achievements.
Rescued 10000 Matter!
Rescued 500 Matter!
Rescued 1000 Matter!
Rescued 2500 Matter!
Rescued 4000 Matter
Defeated 50 Aliens!
Defeated 100 Aliens!
Defeated 250 Aliens!
Defeated 50 Creatures!
Defeated 100 Creatures!
Defeated 250 Creatures!
Defeated 50 Robots!
Defeated 100 Robots!
Defeated 250 Robots!
Completed level 1
Completed level 2
Completed level 3
Searched 5 Red Cases!
Searched 10 Red Cases!
Searched all Red Cases!
Beat the game on medium or hard difficulty
Beat the game on Very Hard difficulty
10 Close Calls during one rescue mission.
Had 100 close calls
Complete level 1 with no upgrades
Complete level 2 with no upgrades
Complete level 3 with no upgrades
Complete level 1 without taking any damage
Complete level 2 without taking any damage
Complete level 3 without taking any damage