Most people already know about world bosses, those godly things like Sword Tamer that many low level players have fallen to. :p
What people don't know as much about are Mini World Bosses. Mini World Bosses are like the solo-able equivalent to World Bosses, given that you're Lv. 90+. While Mini World Bosses aren't quite as profitable, they still drop a plethora of celestones, rare pots, as well as a chance for Chrono Page.
Here is the list of Mini World Bosses:
Strong - 570 474 (Swamp of the Wraiths)
Razorteeth Tyrant - 657 593 (Fragrant Hills)
Snow Bear - 157 732 (Land of the Burning Heart)
Sutrixx - 250 830 (Ancient Wall)
Deiciter Black - 239 934 (Avalanche Ridge)
Deiciter White - 347 938 (Avalanche Mountain)
Desire of the End - 106 410 (Land of Buried Bones)
Earthsharp Clawzard - 104 336 (Land of Buried Bones)
From what I've heard, they take about 24 hours to spawn. Unlike rare pets, these guys aren't as camped, but there are particular players such as ToffeeApple who have a habit of knowing their spawn times. Good luck in hunting them!