Mouseferatu
Hero
It seems to me that it has a pretty good chance of seriously crippling parties of much higher level than 2. And honestly, god help you if you meet more than one.
My 6th-level players (party of four) took on four of them--plus the IDs' backup muscle--and won handily. Honestly, only one person (the aforementioned cleric) ever even failed the initial save. (It helps to have a paladin in the party to grant bonuses.

Point being, IDs are scary, but not as much as they may initially seem.
