Upstairs, you take out the vial. Slowly, you uncork it and look at Mike. "You sure you want to do this?"
"Yeah!" says Mike. You smile and bring the potion to your lips. You drink half of it, then let Mike drink the rest. For several moments, nothing happens - then, your body starts to tingle, similar to before. Mike sighs with pleasure. "Oh yeah, let's do this!" His eyes become a deep shade of yellow. You grin at him, feeling your teeth growing out into sharp fangs.
Your skin itches as brown fur sprouts all over your body. You stare at your hands as your nails become sharper and your fingers grow slightly longer. You see Mike grimacing, clenching his teeth as similar changes happened to him. You notice that his fur is a deep black, a contrast to your brown fur. You groan as your feet change again, growing longer and becoming paw-like. You both feel your ears become furred and pointed, moving to the tops of your heads. Finally, you growl as your face pushes out into a snout.
You see Mike howl with joy, then burst out of the door of the apartment. You grin - he's almost as excited as you are. Time to go off on the hunt...