Here is the full list of all 23 Alien Slayers achievements.
Clear Normal difficulty without moving
Restores 999 armor or health in one game
Acquire all drop items once in a game
Earn over 5,000 gold in a one game
Kill 9,999 enemies in one game
Have 3 Combined weapons in one game
Acquire Gen2 Combined Weapon for the first time
Defeat 100 Bosses
Run the game 5 or more times
Use mutation for the first time
Acquire Gen1 Combined Weapon for the first time
Complete the quest for the first time
Survival success for the first time
Training for the first time
Defeat the boss monster for the first time
All training completed
Apply mutations to all monsters in one mission
Reach drone level 5 in one game
100 games played
Expert Difficulty Cleared