Um. It was me, Servant Corps. I'll cross-post this over to the Dead Chat.
I did it because when I died, I realized there was no Medium, and realizing the Dead Chat would be utterly boring without the Medium, I decided to roleplay as the Medium. I already lost anyway as the Agent Seeker, so I decided why not?
I actually rooted for the Doppelgangers to win, since it would mean I wouldn't have to keep the ruse up longer than possible. I however did console myself in that a Doppelganger could provide an extra fun meta-game challenge if a Doppelganger that died pose as a Townie and try and confuse me. The fact that the Doppelgangers decided not to try and fool me and instead posted huge walls of text to try and intimidate an non-Medium was rather disappointing.
At first, I didn't want to reveal my 'name', but realizing that doing so made me more suspicious, I settled on Masami Phonix, as he seemed inactive enough. It was rather interesting trying to match my rhetoric with Masami Phonix and chaoticjosh's actions. I was also trying to keep up apperances by trying to ease concerns of why Masami didn't reveal himself to be the Medium, and I think I did that quite well.
I disagree with Meph's belief that the Medium would be useful. The Medium has to live in order to deliver the messages to the Town. Once he dies, he no longer have any use. The only reason I was able to form a town base in the Dead Chatroom was that I couldn't die (because I'm already dead). If the Medium roleclaims and somehow get protected from night kills and day kills, prehaps he might be of some use.
And, to finish it off:
"Plus, the Dopps know exactly who is what. I knew you were Medium since... Day 3?"---Webadict
I'm going to treasure this quote. I'm going to treasure this quote for years and years.
And, well, sorry for this. The only way to stop this is to ensure that people don't automatically lose the game. Otherwise, the GM has no power over the person who already lost, and they might do something like this.