Spellcasting Duels Tricks/Tips?

Ok. So I had to do a bit of google research. I found out that both sims must be witches, obviously, and both have to have a spellcasting level of at least 3 to duel with each other. I will assume that's true cause I have yet to duel with any other witch I come across.

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My question is how can I raise another sims spellcasting level. I can't tutor them nor can I buy something that sims will use to increase their spellcasting while using it. At least I havn't noticed an object yet.

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The only idea I have is moving some witches into my house and raising the levels for them and then moving them out. I also read something about master controller but i'd rather keep my game as legit as I can. Anyone have any tricks/tips for me?