The acronym LARP stands for Live Action Role Play. What the F stands for is unknown but it may stand for Fatal. 

The Condesce has Nitram powers to control beasts and since Jade is part dog this makes her vulnerable to those powers. 

All of the guardians knew about the game except possibly for Dad Egbert. It’s stated on this page that Mom was studying celestial anomalies at the request of a wealthy scientist who may have been Grandpa Harley since his company Skaianet made Sburb the game in their universe. 

They would take the Mayor with them to the new universe and rebuild Can Town obviously.

He died when Typheus destroyed Lowas during Jade’s three year trip.

Dave does pacify Karkat many times but they could still be matesprits. 

He traveled to the Medium before he died. The Medium’s timeline began when John entered. 

That was most likely him just being crabby.

In my personal opinion I’m ambiguous to her actions. If she didn’t have him there he probably would get up to some more rascally clown stuff. While her methods are unorthodox, they’re effective in keeping an eye on him.  

He used to the portals in the Frog Temple to teleport into the Medium, get her dream corpse, and bring it back through the portal to Earth.