Jay Verkuilen
Grand Master of Artificial Flowers
]I have no problem putting the fear of the unintelligent undead into my characters with zombie mobs that swarm over people, engulfing them and knocking them prone. That's just par for the course in my Halloween episode.
That's actually a really good encounter. It feels relentless and scary, which all too many combats do not.
It's a question how much does it increase damage potential versus foregoing an attack or two in addition to chance of successfully knocking prone for those monsters that have something more than mush for brains. If I was a better mathematician I'm sure there's a formula there somewhere.
If you don't care about distributions, average damage per round is approximately: (ChanceToHit X Damage) X NumberOfAttackers
So the difficulty is calculating ChanceToHit. Having advantage is roughly +5, I guess you just multiply that times the percentage chance to knock prone and then subtract pushers from the NumberOfAttackers? Hmm...time to break out the spreadsheet. Unless of course you want to get fancy and start talking factorials or Monte Carlo simulations into account.
That's a decent enough approximation for the gaming table. (Note: I have advanced degrees in statistics and a decent enough approximation to answer the question is very much what most of the field is about. You could refine it but it probably won't get much bang for the buck.)
That said, IMO what's really useful is to make things feel threatening and there's nothing like fear of the unknown to do that. Having some of the foes make push attacks to knock prone really scares the players! Having the pushers break through or bypass the line of fighters and get among the casters or archers in back will induce fear and force them to change plans, even if the overall damage isn't necessarily totally optimal.