Grave Lord spawns on the central platform in the Rustling Chapel area of Golmore Jungle after the player chains at least 21 foes of the same type. Initially, the zone does not have enough enemies of the same type to sustain a long enough chain. After clearing the zone of its 18 enemies, Dark Skeletons will emerge from the ground as the player walks around in an endless supply, so meeting the chain requirement becomes quick work.
When the player moves near enough to the center where Grave Lord is after reaching a chain of 21, Dark Skeletons stop spawning. Exiting and reentering the Rustling Chapel allows more Dark Skeletons to spawn, and if the player has not defeated the Grave Lord after doing this, it will still be there.
If the player does this during the Vorpal BunnyHunt, the Dark Skeletons still spawn without the need to defeat the Vorpal Bunny, but the Grave Lord will not spawn when the player chains 21. Dark Skeletons stop spawning when the player has reached a chain of 50. Defeating the Vorpal Bunny resets the chain, allowing more Dark Skeletons to spawn, and the Grave Lord will then spawn after the 21 chain.