Autocast Offensive Spell

Is it possible to make a offensive spell (like firebolt) autocast, that DOESN'T require the unit that is autocast to attack. Is it possible to make a negative heal that only hits enemies?

With triggers, you can do any of that and more. You can't take a firebolt based spell and make it autocast, but you can base your spell on an autocast ability and then trigger the firebolt.
Yes, this is possible. Negative heal hurts and its targeting is workable. Be careful who the damage dealt is from, I don't remember if it just heals negative numbers or if the game registers it as damage. It'd be worth checking out.

I don't neeed it to register the damage, as long as it deals damage!

Use slow or curse as autocast base ability with duration of 0.01, and tirgger the effect in such way that it creates a dummy at caster position, adds the firebolt ability to the dummy and order it to cast it on the base ability target.

About the negative heal ability, please don't base it on heal, because the hardcoded behavior of the autocast won't fit with the desired needs (it wouldn't activate if the target has full heal for instance). So your solution is using slow or curse base abilities and trigger the damage.

Ok, sounds good. I'll prolly experiment around and see what works best.

Heal cannot kill someone. It will leave them at 1hp and continue to autocast on them forever.

well, heal has too many problems, lol, im not gonna use that one.

Heal is fine for targeting though. You could just trigger the damage for as much as that matters, it fires the EVENT_UNIT_SPELL_CAST event and all.

like moyack said, it won't attack if the unit has full HP, and that is troublesome.

It will also only attack friendlies... That could be a problem.
Moyacks way is best.

Try Parasite.