The Alien is a mob that can spawn in the overworld in a 1 of 10 chance in every 10 minecraft days. how they spawn is the structure A.L.I.E.N S.H.i.P can spawn and 5 aliens spawn in there.
the Alien can drop Alien Space ships and if you right click it you go to a new dimension called Alien Planet.
the Alien Boss is found in the Alien Planet Dimension and is found in the Alien Castle Structure. the normal Alien has 50 health and is hostile, the Alien Boss has 80 health and is hostile.