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 breathers 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 forces warp the mind.
Shapeshifters can also change their own bodies into impossible shapes. This is shown in "Kiss of Death" when Elizabeta opens her mouth unnaturally wide, avoids being zoned, and extends her arm to an extraordinary length towards Malik.
According to Bertrand, smoke forces a shapeshifter to reveal its true form.