The Stray Demon is located in the Farron Keep sub-area of the Road of Sacrifices, near the Old Wolf of Farron bonfire. To reach the enemy, simply take the elevator up to the bridge, climb the staircase, and approach it. The Stray Demon walks around on the far left side of the bridge.
During phase 1, the Stray Demon will attack you by swinging his hammer, jumping and slamming into the ground, hurling fiery boulders from his mouth, jumping and slamming into the ground, and very rarely grabbing (which results in death for almost all characters without extremely high health or mitigation).
Hammer swings are relatively easy to read, due to their long wind-ups. Hammer attacks are always singular, or in sets of two (back and forth). The rare grab and occasional spin aren’t as telegraphed, but can still be dodged easily with a backwards roll. The boulders will be spewed for a few seconds at a targeted area.
Once the Stray Demon reaches about 15 or 20% health, he will crumble and become nothing but a torso. His hammer swings are much more furious and quick, but are still easily dodgable. The boulder stream will be much faster as well. Beware the change in attack pace – he will often attack three times with the hammer, catching players off guard.
Since there is no fog wall, you can run from it and escape back down the elevator if need be.