If you are completing the Prometheus Mission Magmatic, one of the hardest creatures to find is the Ashen Drake.
Here is my how to guide.
Map Position: O5
Map Position Start: Start within the Cave. Next walk up to position 1, 2, 3, 4, 5, 6 and 7.
Wait for the Ashen drakes to Spawn.
When you kill an Ashen Drake leave the body and wait to see if another Ashen Drake spawns in and starts heading towards the dead Ashen Drake.
Next head back inside the cave, head back out, and follow the steps above.
Worse case after doing a couple of walk-throughs from the cave to position 7 marked on the map, exit your game and restart your game, and follow the steps again and again.
Total Time to Kill 20 Ashen Drakes: Roughly 3 hours following my process above.