Construction: 22
* Construction (brick): 13
* Construction (concrete): 6
Sandstone: 18
Earth: 12
Marble: 12
Bricks: 11
Abstract: 10
Goldmine: 9
Underworld: 6
Shadow: 5
Tapir: 5
Winter: 5
Carnival: 3
Sand: 1
Other themes haven't been used. Some levels are counted twice, since they use more than one theme substantially.
Data:
100% Built by Lixes: construction (brick)
100 Ways to Die: construction (concrete)
3.1.1.1: sandstone
Alien Invasion: carnival, earth
A long, long way to fall: goldmine
A Matter of Perspective: bricks
Another Lix in the Wall: construction (brick)
A Towering Proposition: construction (brick)
Babylon Fading: tapir
Behind Bars: marble, goldmine
Bibbidi-Bobbidi-Boo: goldmine
Bridges Burning: underworld
Bulldozer: construction (brick)
Buridan's Lix: marble, earth
Buy one get one free: carnival
Changing of the Guards: marble, winter
Charge of the Lix Brigade: sandstone
Chasm: abstract (mostly steel)
Close to the Edge: goldmine
Come on down to my place: underworld, brick
Compression Method 2: marble
Conundrum: underworld
Dances With Lixes: marble, sand
Decompression Method: construction (concrete)
Diggin' The Air: marble, earth
Dividing Three By Two: construction, sandstone
Down Among The Dead Lix: sandstone
Downpour: abstract
Elixir: marble
Escape the Pit: construction (brick)
Eye of the Needle: construction (brick)
Get Hype: tapir
Halfway Down the Stairs: bricks
It's All Uphill From Here: earth
It's a long way up: marble
It's time to climb: marble, goldmine
Labyrinth of Persia: construction (concrete), bricks
Land of Rainbows and Unicorns: abstract
Leap of the Locust: sandstone
Let's all go down the Strand: tapir
Little Miner Puzzle: shadow
Little Viennese Waltz: sandstone, construction (concrete)
LIX: construction (brick)
Lix Lata: goldmine
Lixology: earth
Mice in the Pipeline: sandstone
Minimalism: abstract
No More Heroes: tapir
Oh No, Not Again!: earth
Once you pop, you can't stop!: sandstone
One Step Off: shadow
One Way Segment: goldmine
Prelude: construction (concrete), sandstone, construction (brick)
Quick Turn Around: bricks
Rhapsody--: marble
Riddle Me This: sandstone
Roundabout: goldmine (this is also the only level to make use of changing the background color)
Rumble To The Bottom: underworld, bricks
Segmentation Fault: construction (brick)
Slippery Pete: goldmine, bricks
Subversive Activities: marble
Suicide Attack: abstract
Tapestry: construction (brick), shadow
The Abominable Snowlix: winter
The Adventure Playground: construction (concrete), construction (brick), sandstone, earth, underworld
The Italian Job: sandstone
The Last Laugh: bricks
The Last Mile: sandstone
The Mon0lith: sandstone
The Pit: winter
The Razor's Edge: abstract
The Ring of Fnargl: abstract, underworld (mostly steel)
The Transmigration of Lix: earth
Three Days of the Condor: earth, construction (brick)
Toccata: construction, abstract
Too Close for Comfort: winter, earth
Too Far to Walk: bricks
Top Gear: sandstone
Tribute to Benny Hill: tapir
Vignette: winter, earth
Walk them golden stairs: construction, sandstone
Waltz in C Sharp Miner: sandstone (mostly steel)
We'll Meet Again: bricks, earth, marble
Well OK Then: construction (brick)
Won't Get Fooled Again: bricks
Proxima: Tapir is somewhat redundant due to cvblocks, which IMO looks much better. I could see Simon's desert set working, but Oriental seems like it'd be hard to use outside very specific contexts.
geoo: Stickup is a backroute, but it's a clever (and difficult timingwise) enough one that I'll leave it in. (Also I don't see any way to get it out.) The Fnargl backroute also seems tricky to get out, but this might do it. (I'm not sure if it's that it's not there or that I can't pull it off.)