Nasos
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But I'm afraid to imagine how many times you need to hit a rusty creature for it to start dealing more than one unit of damage.
We're not talking about reducing the target's defense by 3, but about a 20% chance of dealing direct acid damage. Or is this damage countered by defense?
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I had Gorgons in mind, but elemental creatures don't care about their ability, but I didn't think about the rusty ones.