The Mongols could defeat regular armies because they had many thousands of men who lived their lives on horseback, with bow in hand. It's not that they were smarter, it's that they had the option.
The Mongols easily won the Battle of Legnica in Poland: http://en.wikipedia.org/wiki/Battle_of_Legnica
That's really the most Western of their major battles, and they were turned back by choice, not by losses in battle.
Were there any cases where they had anything other than skirmishes with Germanic tribes?