Wow, I ran into one of those with a 12th level fighter of mine. The DM thought it would be funny to put it in a dungeon we were exploring. After seeing it, I ran thinking, 'Hey it's short and small. I can at least keep away from it!'
No way, according to MM those things move as fast as an unarmored man.
It thrashed me in two rounds...it would've been one but it waited until after I was done crying for my momma.
I still get chills...