I was making a class and i decided to make a level 1 barbarian and add a second class to it so i chose to be a sorcerer as well with draconic ancestry and i realized i made a battle magic user that can kill you in more ways than 1 as i can rage, use spells, turn into a part dragon and have a F*@# ton of health!!
So my question is what is more scary with the barbarian?
The problem with multiclassing into a Spell Caster is you can't cast spells while you are Raging and you can't even Concentrate on spells while Raging. You're not focusing on one thing to be good at, spreading yourself to thin.
That said, in my personal opinion. 1-2 lvls of Barbarian and the rest of it Moon Druid is an amazing combination. Moon Druids care almost nothing for their spell slots and the Rage will add to Wild Shape's sustainability.
That said this is all very subjective, because every defines "scariness" differently. For my The Above character I made was very more effective incombat then I ever expected. I was worried I might outshine the party too much, but it balanced out after lvl 3 pretty quickly.
I imagine the scariest multiclass for a barb would be 9 totem barb/2 fighter/9 assassin rogue. You only really need three levels in assassin for the scariness, but you can grab more for extra damage and defensive features. For fighter, pick twf. For barb, pick up elk as your first totem for extra speed and wolf as your second totem for sneaking around more quickly. Wield two rapiers and pick dual wielder for one of your feats. Surprise your enemy and use your action surge for an extra action. Every single hit you make crits. For your first turn, charge up and make three weapon attacks (two from extra attack and one from twf). For your action surge, make make two weapon attacks with your extra attack. If the dude(s) is dead, run off to where people can't easily see you. If you have a cloak of invisibility and drank a potion of speed (add another attack), this is even scarier. If someone pulled this on my party, I would be shitting my pants.
If my math is right, you're doing 20d8 brutal crit with rapier damage + 10d6 sneak attack crit damage + 5x str mod damage + 15 rage damage in a single round if all your attacks hit. Yikes!
In terms of Mechanics its hard to beat the Moon Druid/Totem Barbarian.
But Zealot Barb/Spore Druid would function ok Mechanically, and the visual interactions between Divine Fury (necrotic) and Symbiotic Entity would pretty rad. And 1d6 Necrotic, + 1d6 Poison on hits would be pretty nice...