Blue
Ravenous Bugblatter Beast of Traal
That's what it was! Thank you! Yeah, it's not a huge boost, so I don't think we'll end up changing how we've done it, but I do need to point it out to the DM, since he is more "by the book" than I am when i'm DM.
Sentinel, War Caster, and Booming Blade basically means they cannot escape you unless they're an absolute tank, which is fun. Mix that with Swashbuckler, and at level 9 rogue you're like, hey, come get me, <stab> come on come get me <move away without op. attack>, and they can either follow and get rekt, or not follow and be useless on their turn. It's basically the 4e "chicken-defender" swordmage, but somehow even more mean?
Probably a good thing rogues have no access to the use of polearm master and SA...if there were no weapon restrictions on rogues, a polearm swashbuckler w cantrips would be the most frustrating PC to fight ever.
One additional point is that Booming Blade has a range of 5 feet, so you can't take advantage of reach at the same time you are using it.