Might of the Magus

When a creature rolls a 1 on the d20 roll of a saving throw against a spell you cast that deals damage, they take the maximum possible damage from the dice, instead of the result you rolled.

Whenever you roll a 20 on the d20 when making an attack roll against a creature that creature gains disadvantage on all saving throws against spells until the end of your next turn.

Creatures with the Magic Resistance ability gain no benefit from that ability against spells you cast.