Just saw this Bonnie Tyler remix of the Cadbury Gorilla ad on TV. Wasn't sure what was going on. But according to The Guardian, Fallon decided to mix it up a bit because of all the online mixes that were made in response to the original. They felt this was more interesting than just airing the older ads.
See some more here including Nirvana, Guns 'n' Roses and the Bonnie Tyler one.