Wild Fusion (3.5e Feat)
From D&D Wiki
Wild Fusion [Druid]
Wild Fusion allows the user to lose the your animal companion to become one with your animal.
Prerequisite: Animal Companion class feature, Wis 18.
Benefit: This allows you to gain the memory of the animal companion and trade 3 stats with the animal companion, you will still be able to cast spells, but get -3 to all stats and movement is halved for the period of time the player is getting used to the new body. Then the DM will choose how long this time period is.