Speculah:What is Lord Humungus Doing at the ED
Lord Humungus from the movie Mad Max 2 appears in Episode 2's ED eyecatch. The movie has a post-apocalyptic setting and fighting over scarce resources as a main theme. As a further parallel, it's not just "a resource" that they are fighting over in both Mad Max and Madoka, but "fuel". Petroleum to refuel vehicles in Mad Max 2 can be compared with the use of grief seeds to refuel magic powers in Madoka.
This could also simply be a pun as he is in "Mad' Mag' 2" by mistake.