Before you ask, no this isn't really a crossover but it's as close as we're going to get. Now a week or two ago in reference to the release of the Pacific Rim trailer one ex-screened writer Alex Navarro tweeted the following:
Let us also not forget Del Toro's Emmy-worthy cameo this season on It's Always Sunny In Philadelphia as the patriarch of the McPoyle clan.
Now this caught me off guard, having seen the aforementioned episode (Season 8, Episode 3 "The Maureen Ponderosa Wedding Massacre") but had not taken notice of Del Toro's cameo at all. After doing some digging (by which I mean typing "It's always sunny Guillermo Del Toro" into a youtube search bar) I found a video of Guillermo Del Toro getting ready for his role as Pappy McPoyle.
Unfortunately I couldn't actually find any footage of him in the episode, so you'll have to settle for this image:
Anyway upon further digging, I found out that the reason he made a cameo on the show is because him and Charlie Day hit it off on the set of Pacific Rim which Day apparently has a role in. I'm still trying to wrap my head around Charlie being in Pacific Rim, I mean I love the guy but I don't really see him in any serious roles at any point. I guess maybe he'll be some kind of engineer or janitor for the robots. Either way I just thought this was a cool little cross media cameo that I felt like sharing .
And while we're on the subject of Pacific Rim Crossovers, I'll just leave this here: