I’ve personally found great effectiveness using cloud of daggers maybe more than any other spell. Funnelling enemies through a passageway with multiple cloud of daggers cast on the spot is probably my current meta. Then I utilize thunder wave/ black hole to keep the enemies on the other side of the daggers once they make it through.
Another thing if found amazing success with is getting a party to strength 20 as fast as I can, which then I find 90% of enemies can be thrown off cliffs for instant kills. Throwing enemies off cliffs also only requires stealth checks where the body hits the ground and dies.
Lastly there is a fun little cheese strategy I’ve picked up that I don’t see anyone talking about. If you cancel an improvised weapon attack with an NPC before you deal damage, you can move NPC’s without angering anyone.
I like my ballistic missile Karlach: she’s built for speed. A ring of speed (+3m), aspect of speed (+1.5m), fast movement (+1.5m), longstrider (+3m, so 18m base speed), and boots of speed (bonus action for twice the speed, so 36m). This allows her to go absolutely anywhere on the battlefield and kill the target. With a potion of speed it’s even more ridiculous. She’s the MVP of the group.
My paladin on the other hand is the immortal pillar of the group: armour of persistance, shield, ring of regeneration, cloak of displacement, and defense fighting style. Nothing can hit him. So he can grind any fight and revive who needs to be. He is the backup piece, when Karlach can’t do fast enough.
Of note was the slow spell during my playthrough. This was the best controle spell I could use, because the area it can affect enemies is absolutely gigantic and it completely neuter the enemies. I didn’t use it all the time though, only when a fireball or wall of fire wouldn’t do it. Globe of invulnerability was also key for some encounters.
That’s the height of my first playthrough. I’m not the optimizer kind though.