The Changeling is the final monster race unlocked in the alpha version of Desktop Dungeons. The Changeling can be unlocked by defeating the Boss Hive with four different classes. This character takes on the characteristics of whatever monster he attacks. For instance, if he attacks a poisonous monster he gains a poisonous attack. Monsters without special abilities (or with those not applicable to player characters, such as weakening) do not grant the Changeling anything.
The changeling is the only character from the alpha that has not made a reappearance in the beta.