Sell your soul to multiple Daedra.

Desecrate their shrine.

Become Mercer Frey.

Destroy the Dark Brotherhood.

Join the Thalmor.

Kill ALL and i mean ALL of their priests

DeStroy their artifact

Or, in the case of Sithis, violate any of the Five Tenets. "To do so is to invoke the Wrath of Sithis."

On second thought, I'm not entirely sure Sithis is a Daedroth. Oh, well.

Mention that they are inferior to ANYTHING, if you say, "Hey Nimeria, did you know that Malacath is WAY cooler than you?" You would get roasted on a spit.

Aaliizah

On second thought, I'm not entirely sure Sithis is a Daedroth. Oh, well.

No, Sithis is much older than the Daedra. He is neither Daedra nor Aedra.

Give their amulet to a daedra...

kill a lot of their followers, burn their shrines, and destroy a lot of their amulets

Be Tiber or Martin Septim and either become a god or beat one down.

Phelan1019

Aaliizah

On second thought, I'm not entirely sure Sithis is a Daedroth. Oh, well.

No, Sithis is much older than the Daedra. He is neither Daedra nor Aedra.

He is the void in which everything resides.

Sithis is neither an Aedra nor a Daedra. He is in the void, and he was one of the first things in existence. He basically tempted a normal woman with extreme power, in exchange for killing her 5 babies. She did so, becoming The Night Mother, who started the Dark Brotherhood, in the name of Sithis. Sithis is also usually portrayed as "The Dread Lord", as he is not technically man, Aedra or Daedra, but just spirit. Using The Dread Lord as a person allowed Tamriel to get an image of what he could look like. Phew. Please no more. I'm done on lore. For now.