The narrator of "Monster Wedding!" is hallucinating the whole thing.
He's at a perfectly normal wedding, but cold feet combined with a bad hangover from his bachelor party are making him view the wedding party as a collection of monsters, and his bride-to-be as some kind of spider-woman who wants to eat him. His screaming at the end is him freaking out and running away, not him being eaten, and the ominous silence at the end of the song is just the awkward Stunned Silence of everyone else wondering what's gotten into the groom.The girl from "Plastic Lips!" is a Robot Girl.
It would explain her "shiny vinyl-y" skin, her flawless beauty ("She's perfect, she's plastic"), her intelligence ("She's a genius, did you know?"), and her eccentric behavior ("You know that girl, she's out of touch"). The narrator eventually discovers her secret ("You're really artificial / It's officially official!") but in the end it doesn't change how he feels about her.The narrator of "Monster Wedding!" is the same guy as in "The Man With Glooey Hands" suffering an Ironic Hell.
Both feature some sort of forced romance and involve something sticky (Glue and spiders are known to produce webs). The man with the glooey hands may have had his hands glued to his lady's face, nothing was said for her hands, which were presumably free to either call the cops or kill said man. Either way, he is invited to the wedding by a ghost, who could easily be interpreted as a Psychopomp, and he is damned to spend eternity with an unrequited lover who horrifies him, much like how he horrified the lady in his previous life.The song "The Ballad of Mr. Bonkers" is about a kid showing off his pet scorpion that ends up becoming an absurdly cool talking scorpion thanks to the Power of Friendship.
The song easily has a lot of lyrics implying that Mr. Bonkers isn't at all human and it can be interpreted that said kid is imagining all kinds of stories and adventures about how cool his pet scorpion is at the beginning. The middle part is when the other kids come over to see said scorpion and the kid is making sure his pet is okay, which it is. The final part is about the scorpion magically becoming a giant talking humanoid scorpion who is cool and does all the things his owner bragged about and everyone is bound to have an awesome slumber party with their new friend, Mr. Bonkers.