Here is the full list of all 59 Brutal Legend achievements. It takes around 35-40 hours to unlock all of the achievements on Windows.
Complete Campaign mode on Gentle
Personally smote 300 enemies - any mode
Complete "Sea of Black Tears"
Double Team with every Ironheade unit
Complete "Dry Ice, Wet Graves"
Complete "It's Raining Death"
Complete "Sanctuary of Sin"
Complete "Pilgrimage of Screams"
Purchase 1 upgrade in the Motor Forge
Complete "Battle for Bladehenge"
Complete "Lair of the Metal Queen"
Complete "Exploited in the Bowels of Hell"
Complete "Welcome to the Age of Metal"
Complete all hunting secondary missions
Complete all racing secondary missions
Complete 20 ambush, outpost defense, or mortar secondary missions
Achieve 100% completion on the stats screen
Free 40 Bound Serpents
Free 80 Bound Serpents
Free all 120 Bound Serpents
Purchase all upgrades in the Motor Forge
Learn all guitar solos
View all vistas
View all Legends
Unlock all songs in the Mouth of Metal
Summon all Motor Forges
Win an AI stage battle - any difficulty
Win a ranked multiplayer match
Win 10 match-made multiplayer battles.
Win 50 match-made multiplayer battles.
Double Team with every Drowning Doom unit
Double Team with every Tainted Coil unit
Win a single-player Stage Battle against the AI using only orders
Acquire 3,000 Fire Tributes
Spend 250,000 fans - any mode
Slay 150 enemies with the Deuce - any mode
Gain 5 or more seconds of hang time in a single jump - any mode
Play with or against another player who has this Achievement
Trap 15 enemies in one ring of fire with the Fire Baron's Double Team
Kill 25 enemies with the grinder of one Rock Crusher
Hit 6 enemies with the explosion from a Brood's Double Team
Hit 15 enemies with one Agony Ball using the Pain Lifter's Double Team
Kill 20 enemies with one Bleeding Death
Jump over a Hextadon in the Deuce
Ride one of every ridable animal.
Ride a Razorfire Boar into the Sea of Black Tears and live to tell the tale.
Kill a Tollusk using only Ground Urchins
Complete Campaign mode on Normal
Complete Campaign mode on Brütal
Win an AI stage battle - Brütal difficulty
Run down 20 animals in the Deuce with the Coiling Maw equipped.
Kill 20 Tainted Coil units with the Disgorger.
Kill 20 Drowning Doom units with the Eye of Sorrow.
Make out with Ophelia while wearing the Mountain Man Threads.
Kill 15 enemies with a Metal Beast while wearing the Zaulia Threads.
Play a multiplayer game on all Hammer of Infinite Fate multiplayer maps.
Win 10 games on Hammer of Infinite Fate maps - ranked or vs. the Brütal AI.
Chisel four Razputin heads onto Mt. Rockmore.
Visit the grave of a fallen hero while wearing the Black Metal Threads.