im looking for a game in the style of MD
so a browser game (no download)
with a possibilty to chat and RP freely
with some mystery around it
preferable still in the fantasy branch

(nope not going to quit MD)

Hmmm. I have heard of only one. You can check it out: www.magicduel.com

it's kind of frowned upon to discuss other games within the forum and game.....

Well, yes, but he IS in offtopic >.>

Anyway, MD was made to be unique. I doubt you will ever find another game like it until someone rips off the idea.

There are actually a lot of games with a basic foundation of the stuff you listed, but as far as I have ever seen those are all just text based, with no images anywhere. If you are after something like that, they aren't to hard to find, but the similarity to MD ends after you go past "has chat, use chat to RP, is a fantasy game"