Here is the full list of all 20 Impaler achievements.
Complete all stages and defeat the boss.
Score over 1,000
Score over 5,000
Score over 10,000
Unlock all weapons
Unlock all upgrades
Jump on top of a flying enemy
Deliver an offering without pushing it.
Score 20,000 or more 5 times
Complete the game without gun kills
Complete the game without spike kills
Kill 5 enemies using exploding barrels
Overheat your weapon 10 times during a single run
Slay every type of monster
Stomp and kill 5 enemies at once
Kill 6 enemies during bullet time