What are some ways of creating fancy backgrounds? I would like to make a space-themed background with a random placement of tiles.

use gfill for the different colored tiles, and use sprites for some space themed objects floating around. basically, put the code to draw tiles and move a sprite in a loop along with the code to write the title.

I know how to use gfill to create a simple continuous background, but how do I use it to create a complex background with some tiles being different from eachother? I do like the space object idea, though.

Just use random: RND(N) then associate each random number with the tile you want, same for location.

That gave me an idea! I'll use loops, rnd, and bgplace (That's how you place a single tile, right?) along with bgfill to create a complex background.