I think that simple arithmetic doesn't apply here; instead, a percentage is taken sequentially from the current value. It's a simple idea, and here's how to test it: place, say, a Dryad and surround it with 6 Unicorns. Adding them up, we get 20*6=120% magic resistance, which is obviously incorrect. To avoid confusion, it's best to refresh your knowledge of operations with percentages. And, if I'm not mistaken, the calculations with probabilities are performed in this way: Let's assume a unit has no magic resistance. We place one Unicorn next to it. We get the probability of magic working: 1*(1-0.2)=0.8, or 80%. Now, let's add another Unicorn on the other side. The probability of magic working: 0.8*0.8=0.64, or 64%. And so on. With each new Unicorn, we multiply by 0.8. Therefore, the chance of magic working decreases each time, but it will never reach 0, and certainly won't become negative. :)