Cults, I'll have to be honest, I do not know much about. The Mythic Dawn is what I'll start with.
The Mythic Dawn worship the Daedric Prince of Destruction, Mehrunes Dagon, now, contrary to the the Prince of Destruction, they use Conjuration more than Destruction. Destruction could also be literal destruction, as evidenced by his Realm of Oblivion. Now, the Mythic Dawn are evidently a very sneaky and mysterious type of cult, the Assassination of Uriel Septim evidenced that. However, there are major holes in the offensive tactics of the Mythic Dawn, which is strange, considering their ultimate Leader, Mehrunes. They failed to Identify Martin, the last Dragonborn, and the last link to the Septim family. The Daedra marched in Kvatch, and destroyed it. The Mythic Dawn failed to recognize the great threat of the Champion of Cyrodiil and that foolishly lead to their downfall.
Now, their believes and practices are much different. You see, normally, I would think that the Mythic Dawn would follow Mehrunes Dagon through everything, but instead they follow Mankar Camoran, and they follow his book. Now, the Mythic Dawn, when killed in the service of Lord Dagon, become spirits in Camoran's Paradise, which confuses me. Why go to some loser Prophet, when you can service the almighty Lord Dagon? I'm gonna cut this post short, so I can be corrected, and I will be continuing conversation in later posts.