Arcane Rune Skeleton

Lightning runes:  Depending on the number of runes on the skeleton it gains special abilities.

1 Rune: The skeletons speed is enhanced. +10 ft walking speed, and +5 ft for every rune after.  The skeleton also gains lightning resistance. +1D4 lightning damage per rune to weapon attacks.

2 Runes: The skeleton gains the ability to arc a small lightning bolt to a point it can see.

3 Runes: The skeleton gains the ability to cause a discharge the runes on its body causing one of them to overcharge and explode.

Shortsword. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage. +1D4 lightning damage per rune.

Shortbow. Ranged Weapon Attack: +4 to hit, range 80/320 ft., one target. Hit: 5 (1d6 + 2) piercing damage. +1D4 lightning damage per rune.

Lightning Bolt: Range 100 ft, 5 ft line, DC12 Dex Save, 1D6 lightning damage per rune.

Discharge: Every creature in a 10 ft radius must make a DC 12 Dex Save or take 5D6 lightning damage, half on a save.