I haven't thought of a better name for this project yet, so it's just called Clean Game for now. My intention is to design simple, clean graphics, but make the gameplay interesting. Then if I or anyone else ever gets a chance, the graphics can be enhanced later. That way I don't get bogged down in the graphics never getting back to working on the game.
So far I have:
1. Conveyor belts on which any of my sprites that are affected by gravity can ride like a platform, but the belts are added to the map by simply placing tiles (not sprites). They work well.
2. Worms just crawl along and turn around when they hit a wall.
3. Bombs will show a fuse burning up in about 10 different frames (lasting about 4 seconds) before they explode.
4. Explosions will ignite any ignitable tile next to them.
5. Boxes of explosives will create explosions when ignited, propagating an explosion.
6. Wood piles and torches will create a fire (burning wood pile or burning torch) when ignited.
7. Fire will ignite any neighboring ignitable tile.
8. Bomb throwing Robot will move forward for a certain amount of time, then stop and wait for a short period, then throw a bomb up and forward, then wait another period of time, then continue moving. It turns around when it hits a wall. All of its wait times can be specified as parameters when the sprite is placed on the map.
9. I'm currently working on a sprite that will grow a plant/tree whose shape is determined by the digits of its "structure" parameter, and grows by spawning new tree sprites as it moves and processes the structure parameter.
Most of the graphics are defined in black and white and colored by the frameset so I can create different versions of various graphics by coloring them differently. I haven't done that much yet except to create green and brown ground from the same graphics.
I'm liking the idea of creating ever more complex sprites that spawn other sprites. The bomb robot is a good example. It's a neat sprite because it can spawn a bomb which can spawn an explosion, which can spawn a fire, which can spawn more explosions, so you can get some really sophisticated results out of some relatively simple rules. Maybe at some point I'll make a bomb robot dispensing truck

. I'll probably make some sort of seed planting sprite that can plant these tree sprites.
I wonder how similar my seed idea is to Tanja's. I still haven't been able to get Tanja's game running, unfortunately.