Apparently to defeat him you need to use Ranger (For me) from that you can gain Mana slowly. Or Necromancer...Attack all you like until there is a chance to summon Undead.
I don't know why but i found yellow a rather difficult boss. For me through Dragonfable I would often get to fight bosses I can't beat no matter how much I dtruggle anpd then end up playing a different questline till I level up 2 or 3 times and get some better items and then I try again and manage. I think yellow was hard cause he drained your mana with certain attacks. Other bosses that did this to me were: The boss at the top of the tower in the Shears questline The giant monster that gets out of the rift The final form of the guy who tried to destroy the Nest And many others I don't remember right now, playing without Dragon Amulet can be hard sometimes:)
