Breakaway Pop Hit: The aforementioned "Happy" hit #1 on Billboard's Hot 100 nearly nine months after the movie's release, and it is also a track on Pharrell Williams' 2014 album G I R L, a legitimate, non-soundtrack album. In fact, many people who like the song now don't realize that it was created for a Despicable Me film until someone tells them (or until they see the music video, which has dancing Minions in it).
Dawson Casting: Word of God is that Agnes' birthday party at the start of the second movie is her sixth. In the same movie Margo meets her first boyfriend, so she is most likely 12. Edith is about midway between these two. All three are voiced by somewhat older actresses (several years older, in the case of Miranda Cosgrove).
Also, she returns from the previous film, but in a much more sympathetic role.
The Other Marty: Al Pacino was cast as El Macho in the second film, but was replaced late in post-production with Benjamin Bratt. His name could still be seen on most of the trailers leading up to the movie's release.