Inside the Theater of Pain in Maldraxxus (not inside the dungeon) you'll find the Sword Sorrowbane stuck in the ground and Oonar's Arm
attached to it. Both of them are clickable objects so try to grab them! Too weak? Then obviously you'll need to buff your strength!
- Do the prequests to unlock Au'larrynar's vendor option, buy a Potion of Unusual Strength and keep it in your bags.
- Buy a Strength of Blood from Ta'tru in Revendreth and keep it in your bags.
- Make sure World Quest A Few Bumps Along the Way is active and you have plenty of time to complete it.
- Buy a Scroll of Teleport: Theater of Pain from One-Eyed Joby for 10 Gold or keep your Hearthstone off cooldown and bind it to the Innkeeper close to Theater of Pain (maybe check the location of Sword & Arm inside the arena if you haven't seen it before)
- Complete 2x ballista repairs for the WQ without losing the first buff (10min real-time, so do not log out) to get 2x Battle Hardened (second stack will refresh timer).
- Head to Glutharn's Decay at far east of Maldraxxus.
- Click 4x Edible Redcaps, then instantly use your Scroll of Teleport: Theater of Pain or hearth back to Theater of Pain.
- Hurry up (80% slow) to get to Oonar's Arm within 2min (maybe you wanna use a Goblin Glider Kit on top of the stairs when using the Hearthstone).
- Use your Strength of Blood and Potion of Unusual Strength now.
- Within 25sec click Oonar's Arm for Oonar's Arm and Sorrowbane to receive Sorrowbane and Harvester of Sorrow achievement. Congrats!
/way #1536 51.42 48.47 Oonar's Arm
/way #1525 53.14 41.31 Teleport Scroll Vendor
/way #1536 53.63 47.93 Unusual Strength Potion
/way #1536 37 47 Battle Hardened
/way #1536 76.44 56.72 Edible Redcaps
/way #1525 51.16 78.75 Strength of Blood Vendor
/way #1536 59.73 73.02 Explosive Strength Vial