Witchcraft
Noun
まほう
わぁ、A級の新しい魔法を習得中なの？上手くいけば、万歳ものだね！
Wow, are you learning new A rank magic? If it goes well we should celebrate!
The devil's method is magic and witchcraft. That's their method of doing things, after all.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.