There were two Daves hosting Jimmy Kimmel Live last night, but it’s a little hard to tell them apart. Filling in for the Walter Cronkite of late night while he’s out this week, Dave Grohl delivered Kimmel’s opening monologue and welcomed guests to the show. Or should we say, “Dave Letterman Grohl.” The Foo Fighters front man dressed as a full white-bearded David Letterman in a letterman jacket for Halloween — which is just *chef’s kiss* — but he also announced his retirement from late night after just a few seconds on the job. Even in his brief stint on the show, he still managed to get Kristen Bell to perform “Do You Want to Build a Snowman?” in the style of Metallica. It’s what Halloween’s all about.