Improved fiendish Servant( Champions of Ruin, p. 20)
You gain the service of a powerful fiendish animal servitor.
Fiendish servant class feature,
Add the following creatures to your list of eligible fiendish servants: ape, black bear, boar, crocodile, dire badger, dire bat, dire weasel, heavy warhorse, leopard, monitor lizard, constrictor snake, Large viper snake, wolverine. In addition, any fiendish servant you call has the fiendish creature template (Monster Manual page 107). The fiendish servant otherwise conforms to the rules in the Dungeon Master's Guide (page 183).