The special episodes of Durarara!! did not contribute to the main plot whatsoever, but was able to portray the characters and their interactions in ways that were typical of them. Since the specials weren't a part of the main storyline, it made sense that a few new side characters were introduced for the two episodes exclusively. I also found there to be more light-hearted humor in the specials than in the anime. Overall, the Durarara!! specials have the majority of the qualities that make the anime superb and I would suggest it to anyone who has watched the Durarara!! series.