Only winning Dota 2 matches will earn you MMR. In order to improve their total MMR, players must win more games than they lose. You could just be in the rank range that is most suited to your current Dota 2 skills if you feel trapped in a given MMR bracket in Dota 2. Dota 2 is a constantly changing game, thus learning more about it can help you win more games.
The classic lore says that Muerta is one of the guardians of the world of the dead, which was only briefly mentioned in the Dota 2 lore before. For example, the gate to another dimension is guarded by Razor "Lightning Revenant".