[3.5] Replacement for displacer serpent

[jiriku]

I'm modding the module "Cormyr: Tearing of the Weave" and working on an encounter that features 3 displacer serpents, 2 1st-level fighters, and a 6th level cleric. The NPCs with class levels are easy to optimize, but the serpents I'm kinda stuck on.

Can anyone recommend a CR 2 replacement monster that does something other than making a basic attack that misses most of the time? Bonus points if the replacement has a shadow or serpent theme, but not required as I can always refluff.

[Starbuck_II]

Shadow Asp (CR 1, Fiend Folio): Bite +8 (1d3-2 + poison).
You could add a template to make it CR 2.

Small Shadow Elemental (CR 2, Tome of Magic) has touch attack +2 (1d4 + 1d4 cold)

[jiriku]

Shadow asps are perfect, Starbuck! Thank you.