Croagunk Cola, or Croak for short, is a popular brand of soda. The company sponsors the hit TV show Valiant Knight Skarmory. Drinking a mix of Croagunk Cola and [Pepsi Analogue] will cause a random part of the multiverse to explode.
The ads for Croak have a rather catchy jingle:
♫It tingles like a toxin!♫
♫Your tastebuds will be rockin'♫
♫and your mouth will love you so, oh~♫
♫Our pure Pastoria fizz-♫
♫Just proves we've in the biz♫
♫Of bringing, you joy. Oi!♫
- Both in and out of universe the song was sung by Tangent.