This is asked many times and generaly this is what most threads end in:
In theory the Mongols are skilled enough to conquer a large party of Europe and possibly reach the Atlantic Ocean, but and this is a big but it will probably cost too much for too little gain. Europe, especialy northern Europe, like Germany, is relatively poor, especialy compared to Southern Europe, the Middle East, China, Asia, etc, so there is little gain for the Mongols. Europe's terrain is heavily forested, which is a terrain for which Mongol tactics aren't terribly suited. Europe is fractured and has lots of castles and walled cities, which means a lot of sieges, incredibly slowing the Mongols down. So the Mongols must adapt and be prepared for a long, long battle. So since there is so little gain, they probably will leave Europe alone and look someplace else.