Sorcerer's metamagic:
Heightened Spell
When you cast a spell that forces a creature to make a
saving throw to resist its effects, you can spend 3 sorcery
points to give one target of the spell disadvantage on its
first saving throw made against the spell.
Wizard's school of divination:
Portent
Starting at 2nd level when you choose this school,
glimpses o f the future begin to press in on your awareness. When you
finish a long rest, roll two d20s and record the numbers rolled. You
can replace any attack roll, saving throw, or ability check made by
you or a creature that you can see with one o f these foretelling
rolls. You must choose to do so before the roll, and you can replace a
roll in this way only once per turn. Each foretelling roll can be used
only once. When you finish a long rest, you lose any unused
foretelling rolls.
Rogue's Arcane Trickster:
Magical Ambush
Starting at 9th level, if you are hidden
from a creature when you cast a spell on it, the creature has
disadvantage on any saving throw it makes against the spell this turn.