I guarantee this is old, so maybe consider it a reminder.
After every raid I check the DM arena for a rare elite mob. Being a well geared shadow priest I can solo this rare mob. There are two possible mobs that spawn (razza or skarr) and I believe they are on a 6 hour cd. The reason these mobs are still useful is because they have some of the highest drop chances of orb of deceptions.
Orbs sell for 200+ on my server, and with a port to TB it takes <10 minutes to check up on them every few hours.
Just sharing