This is a glass mug shaped like a moose. It's a replica of one used by Clark Griswold and Cousin Eddie in the movie Christmas Vacation and is officially licensed by Warner Brothers.
Condition note: on the bottom of the mug is printed a copyright symbol which is supposed to be followed by Warner Bros. Entertainment. On this particular mug the word "Warner" is absent. Please see the last photo where a red arrow points to the blank space where this word is supposed to be.