What kind of creatures can you be in runes of magic

By creatures I assume you mean Races, there is currently only two, Elf and human. An Elf has two race-specific classes that humans cannot be, which are Warden and Druid. A Human also has two races that Elves cannot be, which are Knight and Priest. If you mean what you can temporarily transform to, there are too many to count. You can see for yourself by opening the Item Shop (hotkey= /) and going under the Rubies Section. They only cost 5 Rubies.