Basically, you fight in one of the rooms of the mansion. You'll see a random two characters in the BG, with reactions based around the current battle (a la Smashville). You can see Remilia, Sakuya, Patchouli, Meiling, or Koakuma. Very rarely, it might be Cirno, and just Cirno. At a random time between 30 seconds and one minute, Flandre will fly across the screen. She does 20% damage to anyone she hits, with a reasonable amount of knockback. Right before Flandre comes onscreen, there will be a small "ping" sound and an arrow pointing to where she'll come onscreen from. Also, every now and then you might see a random character not normally in the mansion run by in the BG. The run-by character is randomly chosen each match, and it could be Reimu, Marisa, Wriggle, Tewi, Mokou, Suwako, or Utsuho.