There's the bit about Evil not seeing a curse on Shad. Mary is saying she cursed him. Have to consider all possibilities here:
1. Both legit- This is the least likely imo. Why? Because he supposedly saw a curse on Hardy (placed by Mary) confirming Banshee existence. They both confirmed this way back. Now if he didn't see a curse upon checking Shad, they are directly opposing each other. This wouldn't be possible if they're both legit.
2 Evil legit/Mary lying- Next most likely. If Mary is lying, then which curse did Evil see on Hardy? It couldn't have come from nowhere.
3 Mary legit/Evil lying- This is a likely scenario. As shown above, Evil was also behind the actions. His results can be inferred/fabricated based off what has been provided already. I don't recall if Mary explicitly claimed banshee before Evil mentioned it, I honestly can't be arsed enough to check back. Anyway, in this scenario, Mary did place the curse on Shad, but Evil slipped by forgetting that
4 Both lying- A very plausible scenario. That's because the exchange they had could have been rehearsed. The slip still applies, but in this case, they both just got into a corner. Would be a bit too good to be true.
Anway, one of them have to be lying? The safer bet would be Evil, because if he has been fabricating results since, then it's more likely Mary is legit and did curse Shad, but Evil just missed it.