From the Web Addendum vol. 1:


An intangible unit is an immaterial form able to freely pass
through physical bodies. First, a Character with this power can move through
Terrain without reducing its movement due to scenery, and can cross
Impassable Terrain without any difficulty, although the Character cannot stay
inside of them to avoid making a target of itself. For example, an Intangible
miniature cannot stay inside a statue arguing that it can’t be hit there. This
ability doesn’t allow a Character to move through other characters, whether
friend or enemy. Second, being immaterial, the Character is immune to
most conventional attacks. So, it ignores most damage or harm that isn’t
caused by a Magical or Ki Attack or Special Effect. Enemies of a higher level
than the intangible Character ignore this rule, since their greater presence
will allow them to affect the Character. Finally, an intangible unit can try an
automatically escape from any combat without spending Action points. This
capability doesn’t apply if their adversary is also Intangible.