When you gain your first level in a class other than your initial class, you gain only some of the new class’s starting proficiencies, as detailed in each class’s description in “Classes.” Class Features When you gain a new level in a class, you get its features for that level. A few features have additional rules when you’re multiclassing. Check the information about multiclassing included in each of your classes’ descriptions. Special rules apply to Extra Attack, Spellcasting, and features (such as Unarmored Defense) that give you alternative ways to calculate your Armor Class.