It's a magically animated skeleton! By its very nature it's got a degree of supernatural power about it. A zombie still has muscles and sensory organs, but this thing's walking around through some other means. Let that dark magic have a bit more credit than something so easily dispelled by a sword swing.
That's right, skeletons should be a nightmare for fighters to deal with.
As always, this is written with Into the Odd in mind.
The obedient servants of some wielder of dark magic. They shuffle about carrying out the will of their master as if part of his own soul exists within them.
STR 10, DEX 13, WIL 12. Armour 2 (see below), 6hp.
Counts as having Armour 2 only against piercing attacks such as arrows and spears. Swords, axes and hammers ignore this.
When a skeleton would be killed by physical attacks it is smashed into at least two separate pieces. Unless they are kept apart these will reform on the skeleton's next turn, restoring it to full health. Each half will continue to fight but the half without a sword only causes 1d6-1 damage.
The skeleton's WIL is reduced to 0 the magic animating the skeleton is banished and it falls into a pile of bones.