Oonar's Arm
Oonar's Arm is a Shadowlands battle pet found as a clickable object inside the Theater of Pain in Maldraxxus, obtained alongside the sword {item:inv_sword_104} Sorrowbane by temporarily boosting your character's strength.
Oonar's Arm is a Shadowlands battle pet found as a clickable object inside the Theater of Pain in Maldraxxus, obtained alongside the sword 
Sorrowbane by temporarily boosting your character's strength.
Guide awaiting review
Buy Teleport Scroll
Purchase a 
Scroll of Teleport: Theater of Pain from One-Eyed Joby for 
10 Gold, or bind your 
Hearthstone to the Innkeeper near the Theater of Pain in Maldraxxus to ensure quick return access.
Eat Edible Redcaps
Travel to Glutharn's Decay in the far east of Maldraxxus and click 4 Edible Redcap mushrooms on the ground at 76.73, 56.12 to buff your strength enough to pull the arm.
Rush to Theater of Pain
Immediately after consuming all 4 Edible Redcaps at 76.73, 56.12, use your Scroll of Teleport: Theater of Pain or hearth back to the Theater of Pain before the buff expires — the scroll will place you within several steps of the arm.
Click Oonar's Arm
Inside the Theater of Pain (not the dungeon), click the 
Oonar's Arm clickable object attached to the Sorrowbane sword stuck in the ground to obtain the pet.
Tips
When two players both have Oonar's Arm active and stand next to each other, they play a game of Rock Paper Scissors — the winner glows and the loser explodes and disappears.
Oonar's Arm and Sorrowbane are not part of the Treasures of Maldraxxus achievement, so don't expect credit toward it.
The arm can be found on the Auction House if you prefer to skip the acquisition process entirely. See the video guide for a visual walkthrough.
