The challenge dungeons have some of the worst bosses in the mod depending on which one you do.
Royal Guardian Tier 6 Dungeon
This dungeon found in the Unstable Dimension is a tier 6 dungeon. The dungeon contains dangerous levels of mobs, a prince spawn egg, full Royal Guardian Armor and a Royal Guardian Sword. This dungeon is extremely difficult and has formidable bosses. Should not be taken on unless you are prepared.
Queen Scale Dungeon
Although this dungeon is similar to the Royal Guardian Dungeon but more dangerous as they contain different mobs that are stronger then a Royal Guardian Dungeon. They contain full Queen Scale Armor, a princess spawn egg and a Royal Guardian Sword. They however, do not contain a Queen Scale Battle Axe.