[Itse]

Originally Posted by FlameOn

So any idea who the fat blobby monster is inside David's head? Is it Mojo or someone similar?

I don't think Mojo would fit. The blobby monster doesn't really look that much like Mojo (who has plenty of cybernetics including mechanical spider feet, and those iconic huge teeth) and it wouldn't fit the idea of Mojo's character. (Mojo is the leader of a planet/alternate universe with a themes like slavery, television as mind control for the masses, popularity ratings as a basis of government etc.)

I'm not sure any the personalities we've seen are The Monster as such. The whole point of Legion is that he's got a whole bunch of people inside his head. (Hence the name.)

I'll spoilertag some commentary based on the comics, which not everyone will probably be familiar with.

Spoiler!

In the comics, Legion in his childhood accidentally assimilated the minds of several terrorists who killed his stepfather, which drove him crazy and led to him developing at least half a dozen other split personalities. (Which controlled separate parts of his powers.)

Something similar might very well be going on in the series, and I think that would make most sense for story that's going to continue on to second season. I don't think we're talking about a monster in the style of Mojo. Most likely David accidentally assimilated some rather terrible human being at some point in his childhood. (For example his stepfather, who in this series has been portrayed as a pretty effed up guy.) It's also possible he's done this more than once. For example Lenny might be the remnants of his drug addict friend Benny assimilated sometime before David got hospitalized. Even if there is a Monster of sorts, he might not be any of the personalities we've seen.

Another significant part of Legions story in the comis is that one of Davids "evil" personalities tricks the X-men into fighting one of his "good" personalities. That I think is also a possibility here.

In the comics, even at his healthiest Legion has a couple of split personalities that refuse to go away. Considering the split personalities are kind of what makes Legion, that's probably going to hold in the TV series too.

I also think most of what we've seen in the series doesn't take place in the physical world. I think the anachronism is not just a style choice but a hint that what we're seeing is not all real.