A little more insight into the differences between the 3.0 Beast of Xvim and the 3.5 Beast of Bane.
The Beast of Xvim's Frightful Presence ability specifies that it Frightens those affected for 5d6 rounds.
The Beast of Bane's Frightful Presence ability neglects to specify what fearful status condition it inflicts for 5d6 rounds.
The Frightful Presence ability entry in the MM glossary/SRD specifies that the creature description will tell you what it does, and merely states that it can impose the frightened or shaken condition.
I would suggest just having the ability impose the Frightened condition on a failed save, as the 3.0 version does.
The 3.0 Barghest's Feed ability required 8 HD worth of humanoids to gain a HD, just as the 3.0 Beast of Xvim did. The 3.5 Barghest's Feed ability requires 3 humanoids, just like the 3.5 Beast of Bane does. One missing tidbit from both BoX and BoB is that it never mentions how long it takes to consume a corpse (a Barghest takes a full-round action). One way to help rein in the power of a BoX or BoB is to say it takes a reasonable amount of time, given the size of the Beast and the size of the creature it is eating. A BoX Imp would take at least an hour to eat a human, for example. Just make it something that has to happen out of combat, basically.
Kasz recently pointed out there is a feat in Player's Guide to Faerun, for Clerics of Bane, that allows them to, once per tenday (ie - once per week) touch an animal and make it become a Beast of Bane (it then directs you to the Beast of Xvim template in Monsters of Faerun) on a failed Will save. As an added bonus, its extra damage (from its once per day Smite Good ability) is considered Vile damage.
