Head canons

The Floor is Lava

   One day, the Marauders decided they wanted to take 'The Floor is Lava' to the next level. James cast a spell on the floor of the castle to look and feel like lava. It wouldn't kill you, but it wouldn't feel good either. Remus set a charm so that if you fell, you would be teleported to the Great Hall. Sirius convinced him to leave it where your colthes wouldn't go. They compromised on leaving the person in their underwear and robes. Peter set stepping stones all around the castle as an aid, the only thing was that if you stood on them for longer than five seconds you would fall.
   In the morning, the Marauders knew exactly how to navigate the castle, especially with all the secret passages. Several people showed up in the Great Hall (the only place without lava) only half dressed. The Gryffendore and Slythren boys showed off while the Ravenclaws and Hufflepuffs rolled their eyes. The girls hurried back to the dorms to get dressed. With the marauders being the only ones beling fully dressed, everyone knew who'd done it but without proof...
   "James Potter." Lily said walking up to him.
   "Evans." James said.
   "What have you done to the castle?" She asked.
   "The floor is lava." James retorted.
   "I noticed." Lily said disdainfully.
   "May I have your attention." Dumbledore said. "In light of recent events, all the staff would like to say, good luck and... THE FLOOR IS LAVA!"

   The next year, everyone was randomly teleported somewhere depending on who's common room they were in. Gryffendores were teleported to The Forbidden Forest, Slythrens to the Quidditch Pitch, Ravenclaws to the lake, and Hufflepuffs to the Gates. The Marauders were the first suspects, but when a dazed James tried to open a bush like a truck, that idea was quickly dismissed.

   The Marauders loved the game, the rest of the castle learned to love it as they woke up to another 'The Floor is Lava', the third year in a row. By the forth year, the Marauders had perfected the art of getting out of bed without being teleported to the Forbidden Forest. After they graduated and Dumbledore was named headmaster, it became a tradition. They eventually had to stop because a certain Gryffendore didn't much take after his father and walked straight into the lava. It's all good though, the Triwizard Tournament made up for it.