New creature in Summer Update 2008. Because it used to be a weaker monster, and give lots of experience, in Winter Update 2008 it became stronger and less profitable (loot is more rare now) They also glow green slightly.
Mages: Attack them, run them around using Ice or Energy attacks and try to not get swarmed by other Bog Raiders. With more risk you can stand still and just use Strike attacks but their Melee is quite good. This has more mana waste, but less chance you get in a swarm of these, just keep healing, and there will not be any problem at all.
Knights: Use melee and an exori style attack, better stand and fight since the respawn is fast and more can be lured, diagonal is not necessary. Strange as it sounds, a Garlic Necklace is a better choice than Silver Amulet, as it blocks a large amount of their strong life drain and will last longer, while Silver Amulet will wear off really fast due to the fact you're always poisoned when fighting them.