https://www.themoviedb.org/tv/44305-dreamworks-dragons/edit?active_nav_item=regular_cast This is where you edit them. When you edit the person there is a checkbox for putting them on every season.

Not what I meant. Allow me to expand.

When viewing a season level page like this Season 1 page, you can use the top menu Overview > Cast & Crew to get a listing of all cast and crew for that season only. Which is nice. This works for any season from 1 upwards (season 2,3,4 etc) for any series.

However, Specials are numbered as season 0 in the url so this function doesn't currently work. E.g. the Specials season for DreamWorks Dragons is here: https://www.themoviedb.org/tv/44305-dreamworks-dragons/season/0. Each episode has guest stars. But when selecting Overview > Cast & Crew for the Specials season, nothing shows up. No cast, no crew.

This appears to be the case for every TV show. I randomly had a look at the regular cast for Lucifer and there are 8 regulars in the Specials season. However selecting Overview > Cast & Crew for the Specials season still comes up blank.

Now the point about Jonah Hill is that he appears as a guest star in 2 episodes of the DreamWorks Dragons Specials season. Episode 2 and episode 3. However, back at the top level of the series, when looking at the Full Cast & Crew, Jonah isn't listed with the rest of the series regulars and guest stars that ever appeared on the show. I think he should.

These problems seem to be because the Specials season is numbered as zero. And it's the same problem for every series in TMDB. I haven't found a series yet where this works. I think it's a bug but I stand to be corrected if there was a conscious decision to ignore cast and crew from Specials.

I think this is a bug. Even for a show like Star Wars The Clone Wars where there are a bunch of “add to every season” regulars, it shows them for season 1 etc but not for the Specials season. I don’t know where you report bugs but this seems like one.

Also, I don’t think series>edit displays guest stars, unfortunately.

I honestly can't remember what is a bug and what is a choice. I would recommend searching the forums to see if anything comes up and then asking Travis.

Now the point about Jonah Hill is that he appears as a guest star in 2 episodes of the DreamWorks Dragons Specials season. Episode 2 and episode 3. However, back at the top level of the series, when looking at the Full Cast & Crew, Jonah isn't listed with the rest of the series regulars and guest stars that ever appeared on the show. I think he should.

I'm not sure, but this could be by design? I believe including the Season 0 credits used to cause some issues with the number of credits and sometimes negatively affected the top cast.