Does anyone have advice on this concept

[Sir cryosin]

Ok I want a character to run up hit with booming blade then back off enough to it will spend all it movement to get to me. How this works is its wastein the monsters turn by it staying still so it don't take BB damage. Or it spends it trunk just moving to get to me or someone else.

P.s. I would like this to come on asap.

[Specter]

This works best if you're the tank, or have the means to make the monster attack you (like Battlemaster's Goading Attack). Basically, take 2 levels of Rogue for Cunning Action, and then maybe 3 EK levels to get Action Surge and Booming Blade (or any other fighter if you're a high elf).

[Axorfett12]

Well the first thing that comes to mind is the Arcane Trickster rogue. At level 3, you can pick Booming Blade as a cantrip. The rogues Cunning Action would also let you Disengage as a bonus action, avoiding AoO damage as you back up. And since the rogue doesn't get a second attack, you sacrifice nothing by using booming blade over the attack action.

[Sir cryosin]

The problem with just rogue is you get to disengage but you used most if not all your movement to get in to range of monster so when you use your bonus action to disengage you don't have much if any movement. I was thinking of vhuman with mobile. Then going warlock or sorcerer. To pick up expeditious retreat. Later I would like greater invisibility.

[Giant2005]

You can do this with any class by level 4 if you are a Variant Human or High Elf. Take Mobile as a feat, and get Booming Blade from being an Elf, or from the Magic Initiate or Spell Sniper feat. You don't even need Mobile if you do it via Spell Sniper, as you can attack them from 10' away, so you are never even within their reach.

I'd recommend being a Sorcerer, that way you can Quicken and Twin your Booming Blade to be able to use the tactic against 2 or 3 opponents, instead of just 1 each round.

[djreynolds]

Take the mobile feat as a rogue, then disengage if he is without the sentinel feat, and then dash away.

Or play a swashbuckler, and just be a high elf and get a free cantrip.

[coredump]

My initial idea would be to build off of Swashbuckler3, you can attack and leave, and can CA Dash if you need more movement.

But really, you don't need that much movement, it is a party based game. If you go too far, they will just attack your teammate instead.
Also beware, once all the bad guys are in melee, the BB trick doesn't really matter. (Or if they have ranged/spell attacks)