3D model by Jinsters:
https://www.deviantart.com/jinsters/art/PADORU-3D-Model-Download-776247283
He updated his model to 2.0 but this map uses the older 1.0 model.
I've edited Nero's model to make Santa Saber Alter FBX 3D model with Blender but I've deleted the bones. If you want it,
https://skfb.ly/6QXLP
https://sketchfab.com/3d-models/padoru-santa-saber-alter-7d725ba492c0496c90368743fecf1ed5

https://drive.google.com/open?id=1fHvubbvqcH7T1jS5opOuK23qh8GlU2VP
The texture is made crudely on Gimp.
https://drive.google.com/open?id=1o2l72CxT4CFAXatT3NGta0tcHS4IS4Tr

Songs:
https://www.youtube.com/watch?v=UpOnHiz-1P8
https://www.youtube.com/watch?v=IDPOtcT3O_E
https://www.youtube.com/watch?v=O-OdEkCwtRA
https://www.youtube.com/watch?v=JpebHOg6RHA
https://www.youtube.com/watch?v=Pk1I8uEMrP8

Images:
https://danbooru.donmai.us/posts/3356278
https://danbooru.donmai.us/posts/3356276
https://danbooru.donmai.us/posts/3676444
https://danbooru.donmai.us/posts/2937622
https://danbooru.donmai.us/posts/3656780
https://danbooru.donmai.us/posts/2950812 (nsfw?)
https://danbooru.donmai.us/posts/3042824 (nsfw?)
https://danbooru.donmai.us/posts/2682862 (nsfw?)
https://danbooru.donmai.us/posts/2216059 (nsfw?)
https://danbooru.donmai.us/posts/3563220 (nsfw)
https://danbooru.donmai.us/posts/2606691 (nsfw)
https://danbooru.donmai.us/posts/2606692 (nsfw)
https://twitter.com/steamytomatoes/status/1075369666065788928
https://www.pixiv.net/en/artworks/72182045

Font is kringle font.

To open the door, press: when you are in front of Nero at the corner of the map.
Alternatively, someone can die/kill themselves or end the boss wave which will open the door too.
The secret shop is beside the stairs. You have to enter the secret room first.