IGN: "Mac Kills His Dad" may not have been peak Sunny, but I'll say this at the start - it had one of the best title card cutaways in a while. With Mac proclaiming "I'm gonna save my dad's life" immediately followed by the words "Mac Kills His Dad."
Yes, wild-eyed and terrible Luther McDonald (Gregory Scott Cummins) returned this week. Behind bars, naturally. Barely tolerating his son's existence, as usual. And quite fearful that Mac and Charlie were going to get him killed in prison by trying to poke around his his murder case (a beheading, in fact). Which, as you could guess, sent Mac and Charlie out on a journey to inadvertently get him killed by doing exactly what he told them not to do. During which, the two of them got to swap in and out of being the dumb one and the less-dumb one (Charlie had never heard the term "cursive," Mac kept thinking his dad actually loved him).