D&D 5E - What are your tips for making mobs/swarms interesting?

As I DM I've been finding the mobs a slog to run and the swarms boring.

I could treat a large number of rats, for example, as a swarm, with jacked up stats, but then you loose the chaos and uncertainty of having attacks happen throughout the initiative order. I've also tried to using the mob-combat rules in the DMG. The mob rules are good because they give a certain number of hits per turn, saving on lots of roles and ensuring that a mob is a threat even to characters with high ACs. But having all the creatures act on the same turn changes player strategy in a way that makes the combat more boring.

Similarly, I hat how swarms generally have a single attack, making them a danger to a single player at a time. The solution to that is multiple swarms, so, fine. But then many swarm attacks have trouble hitting high armor classes, which is not a reasonable result. Why would a swarm of tiny insects be hindered by platemail? If anything, having a lot of armor would be worse as you can easily shake out the creatures or swat at the creatures that got below your armor.

For mobs, I've gone to using tools to handle large numbers of combatants so they can attack throughout the initiative order. I've used Hero Lab, but now use Improved Initiative. But but I miss the auto hit rules of mob combat. I'm thinking that when there are a large number of combatants, I can have members choose to attack on a lower initiative order until there are enough attackers for an auto hit and they will continue to act together on the same round. That gives the sense of a character truly being ganged up on. So, their may be the chaos rush of, say, goblins, but they will start to cluster together around individual PCs.

For swarms, I've thought that in addition to using a sufficient number of swarms to create a large enough swarm to threaten the whole party and have multi attacks that I would add some special abilities for tiny creatures. First, I'm thinking that tiny creatures can ignore worn armor. Natural armor, or magic armor like mages armor, or bark skin would have full effect, but plate mail, magical or now, would offer no protection against a swarm of ants, bees, spiders, etc. Further, anyone in plate, or chain, will have disadvantage on attacks against the swarm attacking them unless they doff their armor.

Maybe that seems unbalanced, but it would make swarms worthy of fear and more interesting.

Other things to make mobs and swarms more interesting and challenging:

• Give disadvantage to perception checks when engaged in combat with mobs or swarms
• Make communication among the party more difficult with din of a mob battle or the noise of a swarm. If you want to yell or hand-signal a command to another player, you have to make a CHA (performance) check to make your message heard/seen and understood. It would still be a free action. If in a swarm of tiny creatures, make a saving throw or have your mouth filled with the creatures and take a level of exhaustion as you choke on them (or if that's to harsh, a disadvantage on all attacks, skill checks, or saves for the next round.

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