I agree with Sam, Joules & Bludgeon can't be Elemental Slugs, but they can be Guardian Slugs. Because as far Elementals go, there are only 5, but if there is a 6th, I would think that it would be Dark Energy (maybe the Goon).
As for Guardian Slugs, I think Joules could be one, because remember in "What Lies Beneath", the Shadow Clan said something like "it will take time before more Guardians can arrive", that means there could be about 50 backup Guardians in Slugterra. But also remember that, if Joules wants to be a Guardian, he'll have to stay at the Guardian Portal & protect it for a while, just like Doc.
Same for Bludgeon, he can't be an Elemental, but he can be Guardian but just like Doc, he would have to protect the portal for a while.
Plus one other thing, I think it would be impossible for Joules, Bludgeon or any other slug to be an Elemental, if they already have an Elemental Slug ancestor. But unfortunately I can't say the same thing for Doc, cause since he's the Energy Elemental, does that make him the most powerful slug in Slugterra and the ancestor of every slug, including the Elementals. Well, when you think about it, sure if he was ghouled, then almost all hope for un-ghouling the slugs would be lost (cause every existing Slugterran Boon Doc would've been ghouled), but wouldn't it also effect every slug, cause every slug has "Slug Energy".
yes i know it but also could be the first slug in all slugterra because the question is where did the elemetal slugs come from? the creator could make in one movie or episode that joules could be the father of all the slugs including the elementals and also could be a guardian slug at the same time as the father of all slugs
Unfortunately for you that can't happen now, Doc is Joules's and every other Electrical Slug's ancient ancestor, if anything Doc could be the father of all slugs cause every slug has slug energy and Doc is the energy elemental.
Note: Since the Elementals have debuted, it's going to be unlikely that any other slug will ever be as important as the Elementals and that most of the Shane Gang's slugs won't be slung as much as they used to be, unless all the Elementals, including Doc have to be abandoned in secret location so that no one can cause them harm & destroy Slugterra.
joules could be a strange slug they could change sth from his transformation and could be an especial slug that can transform many things it could be with doc and the elementals united the universal slug
I don't really see anyone other than Doc, and Burpy (but that's kinda stressing it) becoming a guardian slug. I mean, other than how powerful they are and how important they are to Eli, they're not really that special in terms of story. Think about it, Doc has the ability to heal Ghouls (plus the whole Elemental thing) and Burpy only because he's and infurnus (if you don't know what that means, look it up) and the fact that he's been with us longer than Eli. Granted that was only for about one minute, but still.