what exactly made the beta kids use the tumor and scratch? isn’t that used only when your session is in danger of failing?

The Tumor is a bomb that spawns in all Sessions as an EXTRA hard Time Limit, in case the Reckoning doesn’t happen or it happens and you’re still sort of there in the Session doing nothing. It’s only meant to be a local and relatively reduced explosion, BUT given the Kids’ Universe was Cancerous, and the sequence of events leading up to its detonation, their specific Tumor pretty much took both Troll and Human Universes and collapsed them into the Green Sun. Rose, not knowing what was going to actually happen, was tricked into thinking it would blow up the Green Sun, which is why they even sent it out into the Furthest Ring in the first place.

The Scratch, though, yeah it’s a reset button for when the Session is totally fucked up. Which the Kids’ Session is. Jack is just like. Murdering everything, and if they hadn’t Scratched, he would have kept on killing them all until there was only Jade, at which point CD would’ve killed her regardless.