Here is the full list of all 42 CubeGun achievements.
Win 100 waves in Arena with full health
Win 20 waves in Arena with full health
Unlock Avatar Animation
Win 100 waves in Arena with no defend device
Win 100 battles in Auto mode
Win 20 waves in Arena with no defend device
Win 100 waves in Arena with only Reflector
Add 100 friends
Collect 19 weapons
Win 100 waves in Arena with health<5%
Combine 4x4 weapon 5 times
Win 100 waves in Arena with only melee weapon
Win 20 waves in Arena with health<5%
Collect 10 weapons
Win 5 waves in Arena with full health
Win 20 waves in Arena with only Reflector
Win 5 waves in Arena with only Reflector
Win 5 different map in Arena
Win 5 waves in Arena with health<5%
Collect 6 weapons
Survive 100 waves in Arena
Win 5 waves in Arena with no defend device
Win 20 waves in Arena with only melee weapon
Kill 100 enemies in Multiplay
Upgrade to Level 40
Kill 10 enemies in Multiplay
Kill 50 enemies in Multiplay
Multi kill 8 enemies in Multiplay
Multi kill 3 enemies in Multiplay
Multi kill 5 enemies in Multiplay
Survive 20 waves in Arena
Win 5 waves in Arena with only melee weapon
Survive 5 waves in Arena
Multi kill 12 ships in Arena
Multi kill 8 ships in Arena
Multi kill 5 ships in Arena
Upgrade to Level 20
Win 50 battles in Auto mode
Add 20 friends
Add 5 friends
Win 5 battles in Auto mode
Upgrade to Level 5