This episode is a sidestory!  Gintama has been involved in many (one-sided) crossovers.  This time, they're working with the Jump comedy manga Sket Dance!  An episodic anime that airs on Thursdays at 6 PM about a group of three odd jobbers with plenty of laughs and tears...  Sounds very similar to Gintama.  As Gintoki warns that the Sket Dan is coming after Gintama, the Sket Dan members appear and offer a challenge!
You should be grateful you even get any 
screen time in the opening sequences,
¡Deberían agradecer de que tengan tiempo en escena durante los opening,
Vocês tinham é que ficar felizes 
de aparecer nas aberturas