Identity is a central theme in A Midsummer Night's Dream. A drop of love potion makes Demetrius and Lysander's true and steadfast love as transient as a dream. Hermia and Helena struggle with the meaning of their lovers' sudden transformation. Bottom is "translated" and given a donkey's head. And Titania is made to fall in love with this "monstrous" creature, half man and half ass.
On the surface, Bottom's transformation seems the most complete, since it is physical. Yet it can be argued that Titania's personality undergoes a greater change:
Bottom's own personality remains outstandingly unimpaired throughout his interlude with Titania; indeed, a large part of his comic incongruity derives from the fact that his desires as beast - for headscratching, belly-cheer, and deferential service - remain so perfectly faithful to his human character. It is Titania, on the other hand, whose humanity is more fundamentally impeached by the entire exchange, for she - not Bottom - clearly cannot distinguish a bestial love-object from a human one. In this sense, at least, Bottom's transformation happens more to Titania than to Bottom himself. The result is an ideological identity of interest between locally dissimilar anmal transformations, all of which offer roughly the same moral: turning a woman into an animal degrades the woman, and turning a man into an animal also degrades the woman. (Boehrer 1994: 129)
Boehrer's discussion of bestiality in A Midsummer Night's Dream.
Bottom's transformation and Titania's wooing of him is in III i 96-194.