Here is the full list of all 34 OmniFootman achievements.
Defeat Valkyrie
Activate "TheUnyielding"
Activate "EliteFoorman"
Activate "Berserker"
Activate "Challenger"
Activate "Rogue"
Deal 5000 damage in one shot
Defeat Deviant Spider Queen
Activate "ThunderCaller"
Activate "Ranger"
Defeat Executioner
Activate "WeaponMaster"
Defeat Stone Devil
Unlock all shields
Activate "Scholar"
Activate "Cryomancer"
Activate "Elementalist"
Activate "BattleMage"
Activate "Paladin"
Activate "Dragoon"
Defeat Royal Guard
Activate "Knight"
Activate "Pyromancer"
Defeat Night Watcher
Activate "Assassin"
Activate "Warrior"
Defeat Undead Captain
Clear the sewer while equiping old sworld
Finish the game with "Challenger" activated
Unlock all weapons
Unlock all spells
Unlock all powers
Activate "Ghost"
Activate "Alchemist"