It sounds like the other player managed to give their hero a version of Wormtongue's Rank 10 power that does the same thing, but this isn't one of the options for Create-A-Hero. However, it might be possible to do it the long way round. (If modding isn't your thing, skip over the rest of the paragraph!) They could have made a mod that let them give their hero this power. Then, once the hero was saved, they could restore the original unmodded files so that they could play online again - their hero would still have that power in the file.
Of course, this is just a theory, and it might not work in practice. You will find there are a few people out there who look to exploit loopholes. My brother came up against someone with a custom map once, only to discover that the map involved his own fortress being completely blockaded by battle towers. Your case might be something similar where the person has found themselves an unfair advantage.
Still, what's the point? You humiliate your opponent to gain a few measly statistics to make yourself look better at the game than you are. There's a word for people like that, but I'd probably be thrown off of Heaven Games for typing it.
Of course, it might not be that at all! If the person who played the Shield Maiden in question is reading this, know that I bear you no grudge whatsoever.
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