Spin classes
Sinister Trigger, Dreadlord, and Shadow Vagrant unlock via the Classes tab spin. Cost varies; check the in-game UI.
Fragment classes
Cursed King (50 Sukuna), Honored One (50 Gojo), and Anti Magic (50 Asta) unlock via Boss Rush floor 40+ clears. Community consensus drop rate is approximately 0.40 per clear.
Compound-drop classes
Awakened Devil EX needs 1 Devil Heart (compound 5.25% per Frostspire NM run, approximately 19 expected runs), Lv. 50, 1M Coins, and the Valen NPC quest on the neighbouring island.
Endgame class
Unrestricted is gated by Lv. 75, 500k Coins, Honored One at Lv. 25, and 10 Heavenly Fragments (Challenge Mode, 5% per eligible boss, 3 bosses per run).