All vampires can turn into a bat and fog, but a shapeshifter can turn into breathers and even other vampires.
A shapeshifter is, according to Bertrand, actually a type of vampire. They can render themselves invisible (even being in the same room as powerful vampires without the latter noticing) and can morph into both humans and vampires. Bertrand said that morphing into breathers and other vampires "can only be done by using forbidden, dark forces" and requires centuries of studying. He also said that dark magic warps the mind.