Campaign: Descent into Avernus

I am playing this campaign soon and have a concept for a character but haven't quite fleshed out how I want to build him. The character is going to be a criminal/outlaw background, sort of a bounty hunter(assasinations)/thief gameplay, you know, convincing someone for a good price for a contract for my character to climb around buildings and rooftops to eventually take out a target from stealth possibly with a crossbow?, and slip away to collect the bounty, while possibly sliding some good stolen loot in his pocket along the way. It is the Descent into Avernus campaign so eventually going to be riding a motorcycle to get around (so need a little proficiency in that). What ideas can you guys come up with along that sort of concept? Creative twists are always welcomed/encouraged! Looking forward to seeing the type of builds people come up with! :)

(I have gotten major Fallout kind of ideas floating through my head on this tough outsider type of character lol)

 Hexblade (3 or 4)/Rogue X sounds like a reasonable idea to me. This is assuming that your DM allows for your pact of the Blade to work on a bow so that you can summon it when you need it. (Eldritch Knight 3 or 4 can accomplish the same thing). Even without the ability to summon your bow, Hexblade's Curse plus Darkness/Devil's Sight makes a potent suite of assassin style abilities Hex Warrior could give you incentive to specialize in Charisma, though likely redundant since dex will probably be highly prioritizes.

Rogue would fill out your abilities. Thief would give you second story work for roof work, fast hands to try to hide smaller weapons (both at 3rd), Supreme Sneak at 9th, Use Magic Device at 13th, and Thief's Reflexes at 17th for an extra first round turn (and excellent incentive to forgo Warlock 4's ASI especially since rogue gets two extra anyway to soften that blow).

Assassin would give a different flavor with better 1st strike abilities from Assassinate plus disguise kit and poisoner's kit proficiencies @ 3rd, Infiltration Expertise @ 9th, Impostor @ 13th, and Death Strike @ 17th.

Arcane Trickster could be another magical possibility if Warlock is not preferred and could be mixed with Eldritch Knight but would require some careful weighing of each class to find the abilities that fit your desired view of the character.

Reading that character concept gave me heavy Dishonored vibes. You could focus rogue and take a couple levels in a caster class (or even just go arcane trickster), focusing on utility spells (like stealth and mobility). I'm thinking spells like misty step, dimension door, spider climb, phantasmal force, and (of course) invisibility. All these spells (except dimension door) are level 2 spells, so you don't need to be too high a level to get going with this build. I'm sure there are plenty of other spells that would work with this build, but those are the main ones I think would fit.

These spells are all on the wizard and sorcerer lists. Warlock doesn't get Phantasmal force, but makes the most sense with the dishonored theme. Shadow sorcerer also feel quite fitting in terms of aesthetics.
As a quick note: Wizard, Sorcerer, and Warlock all get level 2 spells at class level 3, while rogue has to wait until level 7. If you want the spells right away, I would recommend multiclassing into one of the caster classes to get it to 3 early, then focus on rogue. If you're not worried about getting the spells early, then focusing on arcane trickster rogue is fine.

While you could use any crossbow or melee weapon. for the true Dishonored feel you'd want to switch between a hand crossbow and a short sword in one hand, and a spell casting focus in the other. You could event try to convince your DM to let you have a slightly homebrewed short sword that can fold in half to conceal easier.

Warlock and swashbuckler would also be a pretty good one, as long as you can get some quality one on one time you can be devastating.  It would be of great use to have charisma out the wazoo, especially if going hexblade.