Before we get into special abilities, let's figure out the basics so I can get a Homebrews started.
Int is given: 16
Other mental scores are probably within a few points of that.
Agreed, I'm thinking their Wisdom ought to be higher than their Charisma. They don't seem very personable creatures.
Dex should be high. It has fantastic AC, and is blindingly fast with its whirlwind attack. Maybe Dex 20 or even 22?
It could just have good natural armour. If it can extrude combat-protrusions that are effectively the same as a 2-handed sword (4 ft. blades doing 1d10 damage), it might also have skin as tough as steel.
Str seems like it might be slightly above average, based on its 1d10 damage.
I see no strong indicators for Con.
Define "average" here.
Should it be in the same ballpark as a lesser tanar'ri? For comparison, consider the following AD&D critters.
Busen: HD 8, AC 0, 1d10/1d10
Babau: HD 8+14, AC -3, 1d4+1/1d4+1/2d4
Bar-Igura: HD 6+6, AC 0, 1d6/1d6/2d6
Bulezau: HD 7+3, AC -1, 1d4+1/1d4+1/2d8/1d3 or 2d8/1d3 and weapon +6
Elemental: HD 8, AC 2, 2d10 (air), 4d8 (earth), 3d8 (fire) or 5d6 (water)
Movanic Deva: HD 8, AC -1, 2 attacks by weapon (
+1 flame tongue 2H sword)