Designing the head of one of the spaceworms.
I'm thinking once you've killed a space worm, it explodes and new baby spaceworms come out and you have to shrink down and kill those as well. Basically ridding the universe of spaceworms.
So for example once you kill the galactic spaceworms the baby spaceworms might be circling the planets. Etc. and so on.
Also, there might be other enemies.
If you don't kill the spaceworm in time it might destroy the planet.