Arcane trickster 9/ wizzard 3 is what you want . As they both use intelligence.
You go full intelligence and use the internal rapier that Mizora gives to wyll as it uses your caster attributes instead of dexterity and you also get to summon a Cambian with it.
You will get lvl 3 spells and with wizzard you can learn stuff like haste , hold person , fireball etc.
You get advantage from casting your offensive spells from hidden meaning you can open the fight by casing Hold person on 2 enemies with 90%+ chance to succeed and then if you have haste like from potion or someone casts it on you, you can also hit them for guaranteed crit twice with the rapier .
Another option that is really powerful and I used to solo House of Grief on tactician is Sorcerer 6/ Assasin 4/ warlock 2 with Eldrich invocation One with Shadows and Empowered Eldrich blast .
I use haste on myself then ambush the enemy with surprise Eldrich blast which and then blast them with it with 2 actions and quickened spell for guaranteed crits and then use one with shadows to hide and reset the fight so I can surprise them again.
