I once had a GM whose house rules included every battle receiving enemy reinforcements each d4 rounds.
he end there were four factions in the ruckus and it was taking about 60 minutes per round for him to run it.
Actually if combat are long enough that re-inforcement have the time to come you're doing something wrong. NPC aren't stormtroopers who always miss, and PC aren't doing practice shooting. A combat shall be quick and deadly, if you're lucky one hit shall cause an injury, but usually an opponent doing a successful attack roll will at least incapacitate a PC.
PCs that hit 0 HP aren’t dead, they’re just helpless (disarmed, KOed, socially cowed, etc.) Make it clear that nonlethal options are always on the table. [Spiceomancy]
In the same category, once a character lost enought HP to get maluses, I ask them to roll endurance (whatever how it's called in your game) to simply stay conscious, not only it helps preventing stupid death, but make combat faster. I believe some OSR games have a morale roll acting a bit similar
French rpg bloodlust is famous for God Weapon having their own urges but not being able to indulge them without a human bearing the weapon.
Leading to the poor human getting some power based on what the weaponk let them do, while having a weapon begging them to indulge in violence, lust or any other awful sin.
Having a player having the weapon and another one the bearer open the road to pretty interesting roleplay