Doomwalker is a world boss outside the Black Temple in Shadowmoon Valley. World bosses in Outland have a very long spawn timer but it can be worth while to farm them as they can drop some very valuable Transmog items. And if you are lucky you can make 50000g + from just one kill.
The main items to get from Doomwalker is Talon of the Tempest which has a droprate of about 18%. It sells for 20k +++ gold on my server, and i have at times gotten 60k gold for it. Doomwalker will always drop 2 BOE Epics. Most of them go for anything from 1000 gold to 30k gold depending on server and how it looks, since these items are wanted for transmoging.
Since Doomwalker has such a long respawn rate. I like to log one of my toons that i don’t use too much at his spawn location and them log in from time to time to check if he is up. There usually is quite a lot of competition to get to him, so you won’t probably get him every time. Usually i kill him about once a week, and rack up 40-50k gold each time. You can also just wait at his spawn location but this might drive you mad as it can take a long time.
Respawn timers for Doomwalker according to WoW Wiki is:
Tuesday Night, very late (~1-5%)
Wednesday Night (50-80%)
Thursday Night (15-20%)
2 days after previous kill (30%)
3 days after previous kill (40%)
4 days after previous kill (30%)
If you want to learn how to make 30k gold ++ a day with minimal effort, check out the link below :