This Mod is pretty bad actually. I didn't think about it alot, I didn't change alot, I just had this idea and wanted to somehow realize it. It's not compatible with afterbirth and the project is abandoned for now. There is a chance I'll work on it again but it's quite low.

Now, for the actual mod:

It introduces different versions of Treasure Rooms!
(My definition of Treasure room here is that there is one item pedestal inside)

There's the "Forgotten Treasure Room": It needs a key to be opened and there are new stronger monsters inside.
(The normal Treasure room - Screenshots 1 and 2)

Then there's the "Lost Treasure Room": You need to use a key, a coin or take damage to get inside. You also need to use money, a bomb, damage or a key to get the item which is inside.
(The shop, arcade room and cursed room - The other 3 Screenshots)

And the "Guarded Treasure Room": You need a specific number of red hearts to enter and when you take the item you have to fight normal enemies or bosses.
(The Mob and Boss trap rooms)

And all of these use the treasure room item pool of course.

You can have up to 5 treasure rooms per floor and maybe even more, I don't really know.
You can also have Treasure rooms on Womb, Cathedral and Sheol!

What I'll maybe change/add if I ever work on this again:
-More new enemies in the Forgotten Treasure rooms
-Better balancing
-Afterbirth support

Also: Playing with Azazel is no fun