I know this thread is more about damage and optimization combos.
But I just want to say that as a player the thing that freaked me out the most at a fundamental level was when a room full of zombies all grappled me. Just having the DM say "and hes going to attempt to grapple you" over and over and over again.
A single grapple is annoying. But when it was 3 and then 4 on me, my brain frazzled. I wasn't taking any damage at all, but it got under my skin in a way that damage can't. I felt vulnerable and it just magnified with every grab. And then she started trying to Trip me and all I could do was scream at my party in a panic to please save me.
And if you can get a player to scream "save me" with fear in the hearts, then I think you can chalk up that encounter as a win.
Totally. Something similar happened in one of my games, though it was a peasant militia rather than zombies. The players decided to enter a hostile fortress while the main division of soldiers were deployed elsewhere. However, a large group of new recruits were performing calisthenics in the practice yard. A patroller stumbled upon the party and raised an alarm. The tank decided to charge at the recruits to keep them occupied while the rest of the party dealt with the interior. The recruits were having trouble hitting him (+3 ATK vs 20 AC) the first couple rounds, so they ended up surrounding him, then using the help action on each other to grapple and push him to the ground.
The party had wanted to avoid inflicting too many casualties. It was primarily an intelligence gathering mission for one, but I also made a point of describing these recruits as appearing rather young. However, when the commander joined the fray and started pummeling the tank on the ground, the tank called out for help. The sorcerer responded by fire balling the whole lot of 'em. It got the tank out of the grapple with plenty of HP to spare, but it also vaulted the party from enemies of the state to the nation's most wanted criminals, and I think they honestly felt bad about how it all went down.