The Stoneglare Mask is a helmet in Immortals Fenyx Rising that you can find locked away behind a door puzzle near the Observator in the Crashing Rocks area. It will give you +40 percent damage for 6 seconds when stunning an enemy, and after upgrading it will refill 200 percent of a stamina chunk when stunning an enemy.
You can find the Stoneglare Mask when you are making your way towards the Observatory after getting the Jar of Aiolos. Climb some steps and you will notice a lone demon flying over a small pool near a statue. Take it out with your bow, then jump down into the water. You’ll see a small hole in the cliff face. Swim in there, then make your way through the tunnel.
When you come out the back, you will notice three pressure pads to your right in front of a gate. You’ll need to find something to place on all three of the pads. Continue to the right and climb up the cliff and you will find some rocks. Use the Bracers of Herakles to carry them down and place one on the left and right pads.
Stand on the middle pad and the gate will lift up, and you will need to dash forward through the gate before it slams shut. Open the chest inside and you will get the Stoneglare Mask. Turn around and there will be a button beside the door that you can use to open it and get out again.