There is no one school that offers this, you’re just looking for spells that don’t offer saves, or force multiple rolls.

Contagion is good for burning through legendary resistance because it forces 3 saves, same with flesh to stone, except flesh to stone requires concentration. Throwing both on the big bad will force 2 saves a round for three rounds.

The thing is, usually constitution is a high save on legendary monsters. Tag it with contagions slimy doom for disadvantage on constitution saves and a stunning effect whenever you do damage.