They also remind me of trillochs (MM3), which are also incorporeal outsiders.
Trilloch: Small, 8 HD, Str -, Dex 19, Con 17, Int 11, Wis 18, Cha 18
Energon, Xeg-Yi: Medium, 5 HD, Str -, Dex 17, Con 12, Int 7, Wis 10, Cha 18
The death shade falls between the two in HD. Size isn't given, but I think Small or smaller is appropriate. Since it's incorporeal, it has no impact on Strength.
Int is only 2-4, so the other mental stats might need to drop as well. However, as incorporeal creatures (and ones that might rely on Cha-based DCs), perhaps Cha shouldn't drop?
The AC is ridiculously high, so even retaining a high Cha and obtaining a decent size bonus, it probably deserves a really high Dex (like the will-o'-wisp, which is 29).
Maybe Diminutive, Str -, Dex 29, Con 15, Int 3, Wis 10, Cha 18?
That gives an AC of 27 (+4 size, +9 Dex, +4 deflection), only 1 off a straight conversion.