Spellguard –You gain Advantage on Saving Throws against Spells. Spell Attack Rolls against you have Disadvantage. Reflective Shell –A protective shell envelops you. It reflects any projectiles targeted at you to their point of origin. Doesn't affect creatures that don't rely on sight or that...
The most obvious two are Gale and Wyll, who both mention or make use of spells far higher than they have access to in BG3. Gale, for example, uses the sixth-level wizard spell contingency should he be killed, with a mirror image version of him appearing and talking the party through ...