The Rainbow Attack
The rainbow generator showcased in the screenshot is available through questing in Felwood being a level 45-50 zone. You receive the trinket from the quest Open Their Eyes which is a level 46 quest. This trinket does 10 damage per second for three seconds being highly helpful for lower levels. Not really, just kidding. It also increases critical strike rating by 9. The rainbow has a cooldown of 10 minutes.