Best strategy with dwarf king is to utilize burst DPS like fire, bleeding, and bombs to kill phase 1 before he can pump out too many summons. Phase 2 requires you to assassinate monks/warlocks since they are the biggest threats, and you can use your earth wand to help tank the rest. Phase 3 is a breeze if you have a potion of purity and toxic/corrosive gas, and a fire pot/paralytic gas pot helps. Just drink the purity, throw the gasses, and stealth for 20 turns while you watch the king melt. Don't attack to keep the invis, the boss will die from the damage over time and his summons automatically die after he does. A scroll of artifact recharging is helpful for the fight, but with your current hp you will have to rely on some crazy RNG.