It is a pretty strong assumption Puffy will be doing a comedic song. Not unfamiliar territory as their own song "Youkai Puffy" falls into that genre. I skimmed a translated review from Yahoo.jp and they seem favorable and that is favor's Puffy's musical stylings. I sort of dig this sort of thing, even if it winds up being something I do not like. I say this because is shows Ami and Yumi are entertainers and not just singers, which is probably a good direction they should go as they approach the end of their secodn decade as performers.
Thanks to EQ here is a sampling of the third disc, which contains the Puffy track. Skip to the 38 second mark to hear Ami and Yumi's contribution:
(h/t to Bonsai for the initial find, you gave me a great lead!)
P.S. If you feel the need to drop 32 dollars (or so... and I would not...) on a single Puffy track, I recommend CD Japan (as I get a little snippet that goes to support this blog.