Mystic Theurge

Mystic Theurge is the multiclass option when you get both level 5 in Apprentice and level 5 in Novice.

The Arcane Trickster gets a +1 to Social interaction at level 1. They get a +1 to Combat interaction at level 6. They get a +1 to encounters with Undead mobs at level 3, that bonus increases to +2 at level 8. They get a +1 to encounters with Arcane mobs at level 4. They get a +1 to encounters with Fiend mobs at level 7. And finally, they get a +1 to encounters with Elemental mobs at level 9.