Advanced Wild Shape (3.5e Feat)
From D&D Wiki
Advanced Wild Shape [Wild, General]
Using your knowledge of nature, shift into more ordinary creatures
Prerequisite: Wis 15, knowledge (nature) 10 ranks, Wild Shape class feature
Benefit: When using wild shape, you can now apply templates to the creature you've become. To calculate the strongest creature you can turn into, subtract twice the level adjustment (or challenge rating adjustment if no level adjustment is given) from your class level. This new number is the maximum hit dice of the creature you can turn into. If the template adds hit dice (such as the lycanthrope template), they count against the limit as well. Example: A 10th level druid wishes to wild shape into a half-dragon creature. He subtracts 3 (The level adjustment for the half-dragon template) and can therefore shift into any half-dragon creature with 7 or less hit dice.
Normal: Druids can only wild shape into animals, or plant creatures at 12th level, or elementals at 16th