Cleaving Through Creatures

When a melee attack reduces an undamaged creature to 0 hit points, any excess damage from that attack might carry over to another creature nearby. The attacker targets another creature within reach and within 5 feet of the initial creature. If the original attack roll can hit it, apply any remaining damage from that attack to it.

If that creature was undamaged and is likewise reduced to 0 hit points, repeat this process, carrying over the remaining damage until there are no valid targets, or until the damage carried over fails to reduce an undamaged creature to 0 hit points.

This can also be made to accommodate ranged attacks, where the damage carries over in the same line created by the shooter, still hits the AC, and deals damage.

Example of a Good Cleave

Example of a Cleave Broken by unable to hit Enemy AC

Example of a Cleave Broken by Lack of Reach