The first floor of the Haunted Mansion is mapped below. There are 4 points of interest, listed below the image.
1) This is where you enter the Haunted Mansion.
2) There are some chests here. The first suit of armour also contains an item.
3) There are 2 chests with armour here and the middle suit of armour along the wall contains an item.
4) These are the stairs to the next level.
There are 5 points of interest on the second floor.
1) This is where you come up from the first floor.
2) In this hidden area (go down as if there is a hidden door at the top of this area) there are 2 Tomahawks.
3) Some chests with items.
4) Some chests with Elixirs.
5) Up to the 3rd floor.
The 3rd floor isn't as big and doesn't have enemies. You'll enter into a Save Zone immediately. Touching the blue flames will heal you and give you full magic. Save and exit to the right.
Walk onto the platform. You'll notice a white arrow flashing downward. Press down (either the Down key or on your DPAD or joystick or tap the screen where the arrow is) and the platform will move downward. Go South and exit onto the balcony. To the right is a Bolt Scroll. You'll need this.
Go back onto the platform and it'll move up then to the right. Move to the right, up the stairs and onto the roof.
Go left across the roof. On the left edge there's a chest with an Elixir. Now go to the stairs at the top left of the roof.
Head all the way down each set of stairs into the basement.
You'll head down, then right, then up. Partway up you'll find the first boss. You'll need to hit him with your Tomahawk and Bolt spell while staying healed up.
After defeating the boss, it's back to Riverside.