The Secret Behind the Hidden Map's Background

If you look closely at the background of the hidden map... you can see the figures of fields that were heavily modified in past collaboration events and later became the lairs of sealed bosses, depicted as paintings on easels. As far as can be identified... From left to right: ・Oomori Shrine ・Sakura EX Tree Observatory ・Demon Realm, Ekkken Corridor, Second Gate ・Castle of Reincarnation or Enma Palace