Help creating a necromancer based on crowd control with grappling minions

Hey all,

I've got a bit of a weird request for you. I'm looking to create a Green Dragonborn that uses undead and their immunity to poison to take on large amounts of enemies. Specifically, I'd like to send Zombies and the like into a crowd of enemies, have them grapple and lock down as many as possible, and then use Dragon Breath, Cloudkill, and other similar poison abilities to wipe out enemies without harming the undead. I need to get some level of mileage out of this build, so if it's a totally inapplicable concept I'll just scrap it, but I was curious to see if you guys would know anything about going about this. Doesn't have to be a Necromancer, though right now I'm looking at Cleric 1/Wizard X. Undying Warlock would be perfect if it didn't suck benefit-wise. Campaign will probably be low-to-mid level. The thing I'm currently on the hunt for is a way to increase the chances of each minion succeeding the grapple, but anything works. Thank you for your time. Any advice, experience, or recommendations are appreciated.