Will Ferrell decided that Coldplay needed more cowbell. So he provided it.

When it came time for “Vida La Vida,” Will Ferrell appeared onstage to add more cowbell. Over the weekend, Chris Martin of Coldplay performed at a charity event at the Greek Theatre in Los Angeles during which he not only went through acoustic versions of Pink Floyd’s “Comfortably Numb” (accompanied by Chad Smith and Josh Klinghoffer of the Chili Peppers, Brad Paisley, Duff McKagan of GNR, and Pearl Jam’s Mike McCready–see below for the video) but also some Coldplay material. He shows up at around 2:15 into this video.
So he provided it. Will Ferrell decided that Coldplay needed more cowbell.