You guys remember Jay's "loony" ex-wife and Claire and Mitchell's mother, DeDe Pritchett? Of course you do (kind of hard to forget that). Well, Shelley Long (Cheers) will be coming back to reprise the role in an upcoming season 2 (early 2011) episode:
The former Mrs. Pritchett will make her comeback just in time for little Lily's birthday, and will have another "episode" herself similar to the one in "The Incident".
Source: TV Guide