The Archmage is a roaming Boss found in areas inside the castle at Emerald Isle.
Fighting Archmage is very similar to fighting a protector, but Archmage has much higher stats. The robes average around 30 dr with 90 bc, a blue book will add an extra 10-15 dr at 90+ bc. The red book adds about 30-40 slash dr, 20-30 pierce dr, and 10-15 bludge dr at 50-60 bc. Therefore you will want a powerful bludge weapon (minimum 54, preferably in the 60s) to fight Archmage. Archmage is capable of dealing all 3 damage types, he crits often because of his high intelligence and is able to hit in the low 60s. Make sure to have a runner, and a nice set of full prots on both the runner and the hitter(s).