So I recently read Fazbear Frights, book 9, where the three stories are "The Puppet Carver", "Jump For Tickets", and "The Pizza Kit". Obviously, this story is based on "Jump For Tickets" (I'm calling this the Tickets AU). If you haven't read the book, I'll give you a summary. Colton was a teenage boy who loved mechanics and technology, mind you, he was very good at it as well, and he was also cold and snappy (Sound familiar, anyone?) since his father died. He would go to Freddy's every now and then to gain tickets for a prize he was saving up for, a new gaming console. There was one game though that he found was rigged to favor the little kids and only give the big kids a few tickets; the Ticket Pulverizer. He thought he fixed it once, but it stayed the same. After that, he became obsessed with fixing it so he could get all the tickets. He studied it and made notes on it for weeks, not focusing on school or anything else; he considered anything besides the Ticket Pulverizer an "Unwanted obstacle". Eventually, he believed he was ready and snuck into the Pizzeria before it opened. The clown mascot there, I can't exactly remember his name, followed Colton around, trying to stop him from touching the Pulverizer. Colton pushed him down and got into the machine. Let me give you a quick layout: There was a glass casing around a jump pad on the floor, and the only way to get in and on the jump pad was to either pay four tickets or if it was your birthday you got a turn for free. Underneath the jump pad was the space with all the mechanics, into which Colton was crawling. When someone jumped on the jump pad, it would go down and initially would crush anything under it... So Colton was in the mechanics area, and the clown tried to pull him out, but Colton kicked him away and shut the compartment door behind him. He managed to "FIX" the machine, and when he turned to get out and pushed the compartment door... It wouldn't budge. Colton was stuck underneath there. He forgot to bring his phone in with him, so he was completely stuck. No way out. The clown was pacing outside, waiting, while Colton was trapped. He was there for a few hours, and then Freddy's opened. He tried yelling for help, but his voice was dry and cracked from misuse and dehydration. The children got into the Ticket Pulverizer. He banged his hammer on the bottom of the jump pad and screamed for help. The shouts of excitement from the kids were too loud, and nobody heard his cries. The clown: "Everyone ready? Ten, nine, eight, seven, six, five, four, three, two, and... one! Now... Jump! For! Tickets!" So, Colton got crushed when the kids started jumping. When the jump pad wouldn't go down, Bella, one of the kids, complained to her dad that it wasn't working. The dad got a staff member, Ted, and Ted jumped on it a couple of times to check, and sure enough, it didn't budge, but he thought he heard a faint squishing sound... But that couldn't be right, could it? So Ted got out, and the clown, whose face was normally a comical grin, was a tragedy face, with a tear rolling down its cheek. One of the kids, Colton's annoying, overly-loving little cousin, Aiden, came up and said to the clown "Don't be sad! It's not good to be sad. My cousin Colton is sad all the time, and that's why I'm saving up tickets to buy him a present!". Then Ted got a sign that said "Out of order" and put it on the Ticket Pulverizer.
Imagine this exact story except with Cosmo instead of Colton. And switch around a few other characters. For instance, Colton's mom would instead be Cosmo's brother, of course, as Sun. Aiden... Not so sure, maybe Lunar Eclipse(New character, introduced to a few people)? Ted would be Moon, for sure. Ooh, and Colton had an uncle who was also into mechanics; maybe the uncle is Solar?