Find a super secret
Complete Farewell to Arms on any difficulty
Kill yourself 10 times in single-player
Complete Post Mortem on any difficulty
Find the secret level in Post Mortem
Complete Even Death May Die on any difficulty
Complete Ghost Town (E3M1) on any difficulty without any Innocents getting killed
Kill a Choking Hand
Find the secret level in The Way of All Flesh
Complete The Haunting (E2M5) in under 40 seconds on any difficulty
Find the secret level in Cryptic Passage
Complete Dead Reckoning on any difficulty
Find the secret level in Even Death May Die
Kill 100 Cultists
Find the secret level in Farewell to Arms
Defeat the 3 Beasts of Beauty and the Beast (E6M8) in under 3 minutes on Well Done difficulty or above
Exploit the Hellhound's greatest weakness
Find the secret level in Dead Reckoning
Complete Cryptic Passage on any difficulty
Complete The Way of All Flesh on any difficulty