You'll have your first TrapDoor encounter rather quickly, guarding the room south of the entrance. This room contains a Kotetsu, which is a nice upgrade for Edge. A second TrapDoor guards the northwest room that leads to B2F. Both of these will turn into Mantcores if dropped to low HP. Their Blaze attack is brutal, they have a lot of HP, and they absorb the basic Elements, making them a tough fight. Two more TrapDoors that lead to empty rooms are within this stair area, along with a pair of chests. They're worth fighting anyway just for the experience.