Rotom is literally one of the few Ghost pokémon I find awesome now (All the back when Haunter and Gengar acted as a Manzai duo XD), such a bundle of awesomesauce in one little spark-like ghost.
Piplup kind of annoyed me in this ep, but it's a "mascot" now, so no need to be annoyed with it. It's doing its job.
And I believe that the Old Gateau is like a publicity thing, you know, like how Burger King has Whoppers, McDonalds' McFlurries, even Wendy's Frosties. It's a thing to get people to want it. Why Old, who knows. I guess it makes grown men cry for the taste.