I think that's an interesting take on combos, actually. We had a big discussion about combo systems back in beta but never could come up with something that wasn't cheesy.
However, coming up with some special effects for particular spells would be really interesting:
- Shoot some fire projectile into a tidal pulse, and it gives off a steam cloud that combines the damage of the two plus bug in an area of effect.
- Shoot any spell through a creeping death spell and the other spell takes on the entropy element and gets the damage of the creeping death added to it; but the creeping death itself is destroyed in the process.
- Shoot rocks to set them on fire, like you note; a weaker form of meteor.
- Shoot lightning spells into tidal pulse spells to destroy the lightning spell but give the damage plus 1.25x damage to the new lightning-y tidal pulse.
That could actually work out interestingly for enemy spells, too; if you accidentally hit an amoeba's attack with your ball lightning, then that amoeba's water shot is suddenly supercharged as it comes toward you. Etc.
That sort of interaction is complex to be sure, and I think that there are bigger fish to fry in the very short term. But longer term if we had time to really sit down and design this out, I think it could be really interesting. The risk is getting Magicka-style super spell effects that just everybody uses, but it would be interesting to explore.
Welcome to the forums! Awesome first post.