Calling on your vampiric origin, you can transform into a bat for up to 10 minutes once per long or short rest. To transform, you must declare "Bat!" and then hop in the air. To return to humanoid form you must land and declare "Humanoid Form!" These words must be said in your best Matt Berry/Lazlo Cravensworth impression.
When you assume the bat form, everything you are wearing and carrying blinks into the Ethereal Plane, following you wherever you travel. When you resume the humanoid form, all of your clothes and carried items re-appear on you as they were before.
As a bat, you have a walking speed of 5, and a flying speed equal to your humanoid walking speed. All other statistics remain the same, including your Armor Class. You cannot talk, but may attempt to communicate with other, non-animal creatures through squeaking. You can communicate with other animals, which could be useful if you end up being captured by animal control and want to stage a coup. If another non-animal creature has "Speak with Animals," it can understand you, but your voice is very high-pitched.