Hello,

Try this ApplyRules("ZombieGiant Damage += X%")

Replace X by the amount of damage you would like. Keep in mind that spaces are important between each variable you are calling in an ApplyRule. Let me know if it worked!

In my testing, spacing has not seemed to matter. I have many other pieces of code modifying unit rules that work just fine with no spaces so I'm not sure why this matters. Is this just a general suggestion, or is this a dev recommendation? For example, see what works and what doesn't work below.

Oddly enough, when I try to use what you suggested, I get the "bad arguments" error. https://imgur.com/a/fQ33DLg

This works:
ApplyRules("ZombieGiant Life+100000; ZombieGiant RunSpeed+100000")
ApplyRules("Ranger WatchRange +1;RangerVeteran WatchRange +1;RangerAttack ActionRange +1;RangerAttackVeteran ActionRange +1")

None of these work:
ApplyRules("ZombieGiant Damage += 100000")
ApplyRules("ZombieGiant Damage = 100000") <-- tried statically setting value
ApplyRules("ZombieGiant Damage += 100%")

ApplyRules("ZombieGiant AttackDamage += 100000")
ApplyRules("ZombieGiant AttackDamage += 100%")

ApplyRules("ZombieGiant Attack += 100000")
ApplyRules("ZombieGiant Attack += 100%")