Sin’s Mystery Doors (I need help)

When you enter Sin at the end of the game, you find a city-looking place in him. Some of you may have noticed a glyph on a wall in the beginning of that area. When you touch it, it says:

Ten fiends still seek eternal repose

I figured "What the hey, maybe something cool is back there." I killed on off each kind of fiend in Sin’s City and returned to touch the glyph. The glyph spouted off some nonesense about Yevon and the wall opened revealing…
Another glyph. Glyph says:

Ten fiends still seek eternal repose

"Dude! It must be really cool!" I go kill all the fiends again, touch the new glyph and-

Fourteen fiends still seek eternal repose

What in the world is behind door number three? And why is it "fourteen" fiends now? Have I released four new breeds? Anybody know what I’m talking about?

…

I need help.

Behind door number three is a level four key sphere. Whoopee…