this interaction seems bugged … either that or it is a huge miss in terms of design … i know there are cards that will allow you to pull a spell out of your deck and put it into your hand even if it is a cast when drawn card, but magatha seems to draw cards normally and then apply its “if it is a spell give to your opponent” effect … this is bad/stupid for two reasons:
#1) plagues … magatha would be just about the only card in the current meta that could deal with infinite plagues … there is tony also but giving magatha’s drawback a unique positive case makes her a much more appealing card to consider including in this meta and gives u more than just one option (aside from getting a random card from the past from some classes, but that’s so infinitesimal in standard it’s hardly worth mentioning)
#2) it overly punishes you for a card that’s already risky to play and does not reward creative use of things like trying to mill your opponent by giving them faldorei spiders of hodir giants (or even just something like soul fragments in wild)
it would be great if this could be fixed so that the “draw” function happens last … maybe it would need to be reworded to something like “reveal the top 5 cards, put any spells in your opponent’s hand, draw the rest” … seems really silly that the card text gets overridden by the cast when drawn effect to require this kind of wording change tho