Well, maybe this could help kick start things? I did not write this up. I believe I pulled this from an old WotC conversion thread back in the 3.5 days. I only have the mechanical effects and this was sort of my cliff notes version that I used years ago when I ran some of these guys in an encounter. I don't know how accurate this draft is, but here you go...
Reave
Medium Monstrous Humanoid [Extraplanar]
Hit Dice: 2d8+4 (13 hp)
Initiative: +0
Speed: 20 ft. (4 squares)
Armor Class: 19 (+2 NA, +7 Half-Plate), touch 10, flat-footed 19
Base Attack/Grapple: +2/+5
Attack: Longsword +3 melee (1d8+3/19–20)
Full Attack: Longsword +3 melee (1d8+3/19–20) and 3 Short Swords +3/+3/+3 melee (1d6+3/19–20), or Halberd +3 melee (1d10+3/x3) and 2 Short Swords +3/+3 melee (1d6+3/19–20)
Space/Reach: 5 ft./5 ft.
Special Attacks: —
Special Qualities: darkvision 60 ft., low-light vision, Odd Symmetry, Astral Fading
Saves: Fort +2, Ref +3, Will +3
Abilities: Str 17, Dex 11, Con 15, Int 8, Wis 11, Cha 9
Skills: Listen +2, Spot +5
Feats: Multiweapon Fighting
Environment: ?
Organization: ?
Challenge Rating: 2
Treasure: Standard
Alignment: Usually Lawful Evil
Advancement: ?
Level Adjustment: ?
Odd Symmetry (Ex): Cannot be flanked due to odd body symmetry.
Astral Fading (Ex): Full round action, can shift to the Astral Plane for 6 rounds. Can shift back to original location 100 yards away from original position as a full round action. The Reave is aware of what happens while in the Astral and gains the incorporeal type.