You can copy in the good ones from the LD10 theme list or add new themes! As a general rule, try to avoid themes that either require specific cultural knowledge (including sports), or impose implementation limitations (like “2-bit color”).

• Anti-Gravity
• Aquarium
• Backwards
• Balancing act
• Bleeding / Leaking
• Bumper cars
• Cliches personified
• Counter-attack
• Cooperation
• Defense
• Detective
• Double entendre
• Duel
• Educational
• Endless
• Escape
• Everybody Wang Chung Tonight
• Flood
• Freudian slip
• Gas
• Hats
• Higgs-bosons
• Hunger
• Icicles
• Invisibility
• Jello
• Kittens
• Kisses
• Links
• Livestock
• Lose to win
• Math
• Minimalist
• Morph
• Neutrality
• Ninja
• Nightmare
• Overloading
• Particles you can't see
• Procrastination
• Quirk
• Radio
• Retro futuristic
• Rewind
• Slowed time
• Slipstream
• Tree
• Turn Based
• UFO
• Variable
• Weakness
• Were-things
• Xenomorphs
• Yeti
• Zap
• Zombies

(let's not use these again for a while)

• LD10.5: Weird/Unexpected/Surprise
• LD10: Chain Reaction
• LD9: Build the level you play
• LD8.5: Moon, Anti-Text
• LD8: Swarms
• LD7: Growth
• LD6: Light and Darkness
• LD5: Random
• LD4: Infection
• LD3: Preparation
• LD2: Construction/Destruction (Minor Theme: Sheep)
• LD1: Guardian
• LD0: Indirect Interaction

• PW6: Robot
• PW5: Twisted
• PW4: The only way is up
• PW3: The Disappearing Act
• PW2: It runs on steam!
• PW1: Power

• 72HGDC #8 Nov '06: Magnets
• 72HGDC #7 Jul '06: Retro
• 72HGDC #6 Mar '06: Magic
• 72HGDC #5 Jul '05: Horror
• 72HGDC #4 Dec '04: Swappable Parts/Customize?
• 72HGDC #3 Jun '04: Pirates
• 72HGDC #2 Jan '04: Food
• 72HGDC #1 Jul '03: Mindless violence

• FGDC4: Ball Physics
• FGDC3: Replay
• FGDC2: Grow
• FGDC1: Point & Click