We noticed that there were some questions around the core category so we edited the page to try and clarify as well as add new information.
The prizes provided by Core are exclusively for Core games, so in order to qualify for their prizes you would have to make a multiplayer game in Core. However the challenges are 100% optional. You can still participate in the jam without using Core, and your game may still feature in our after jam video, so long as it's based on the jam theme.
Hope that helps answer your question! - A