The biggest thing that impacts size is whether a rider can ride a steed. If a rider is too large or too small for a steed, they are unable to ride it. Creatures can be small, medium, large or huge. This has an impact on combat, when taking injuries to body types. It also makes also makes a difference to the size of corpses or the amount of material an elemental breaks into when it is destoryed.
Examples of creatures that are particularly small:
bat chicken dark elf child elf child fly fox helicopterum imp jackal rat raven snake spider vulture
Examples of creatures that are particularly huge:
black dragon black naga bone dragon Evil God Adoxie fire demon green dragon ki-rin red dragon red naga skeleton king tree spirit white dragon white naga yellow dragon yellow naga zombie king
Other items in this section