Here is a list of levels made with Diamondus Beta(excluding upcoming ones)

Garden Brawl
Bay of Diamonds - XLM
Christmax - XLM
Crematoria
Diamondus Warzone Beta
Darker Insomnia
Overheated and Freaky World - XLM
The Unnamed Level
Even Darker Insomnia
Forest of Diamondus
The other side of Diamondus
It's Over - XLM(when P4ul was still in XLM)
Hot Springs
The Forest at Night
Rocky Gardens - XLM
Midnight Battle - XLM
Cutted Problem - XLM
Dusky Siegeness - IC
Diamonds of Diamondus
Holy Gardens(3-level pack)
Diamondus Midnight
The Lost Battle Game - IC
Some level from AB Single Player Pack 1
Chlorophyll World
Forest Burn - XLM
The Highlands - XLM

Not counting the upcoming levels.. well, I have even more Diamondus Beta levels. As you can see, XLM used it quite some times but some levels were one of the first levels with the tileset. But there are also lots of levels that are not made by XLM or IC ;p. Only 9 XLM levels, and none upcoming(I think)