Hey guys, I set a unit's attack to 0 but I noticed it still does damage. Is there a way to totally negate a unit's damage?

Hallucination.
Weapon sprite limit (so many units shooting at once that there's no sprites left for the ranged unit's attack animation). Drawback: Affects all units and some random shots will still occur.
Otherwise no. Attacks will always do .5 damage.

If it's only one specific unit type that is the target, you can set it to 0 hp maximum. That way, all attacks will deal no damage to it.

For units with shields and a high armor value, say 1/1 shield (+10) and armor (+50), attacks that deal less than 62 damage will not hurt the HP of the unit, even though you would assume that 0.5 damage carries over from the excess damage.

EDIT> you know what, just give a unit 1/1 +65535 shield when invincible.

shields only go up to 255 upgrades.

I remember somewhere from the wiki that armor can take on 255 * 255 upgrades + 255 base for a total of 6553565820. I never figured out how it worked though, and I can only give 255 shields/armor at the moment.

Armor isn't multiplied. it's added.

Attack is multiplied:
0-65535 base damage
0-65535 damage per upgrade
0-255 upgrades

There's a hard limit of 65535 damage on both base and upgrade damage, so if you have 7 upgrades each at 9999 damage each with 100 base damage, you'll do 100+4457. It's sort of like how if you upgrade armor to 255 and have chitinous plate armor on ultralisks, they have 2 armor.

Armor has a set 1 armor per upgrade. Shields have no base armor.