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