So far it is a psychic / ghost type that is 600 kgs, has a head and upper limbs and is purple
Unnerve or Intimidate I guess?
When it enters battle it causes an earthquake because of it's weight
It is immune to everything
Truant
Because
Either Infriltrator (Spiritomb's Ability) or Wonder Guard (Shedinja's Ability)
What do you think?