Type, stats, ability moveset

>>32011591
Ghost/Dark (or Ghost/Psychic, if you'd like that more)
Ability: Unknown veil -The opponent does not know the name of the attacks used by this pokemon

HP-200
Atk-70
Def-60
SpA-180
SpD-100
Spe-70
(680 BST)

>>32011624
Gyigas isn't intentionally evil or ill-meaning, so Psychic or even pure Ghost would fit it better but with access to Dark and Psy movepools.
Add to Unknown Veil: Attacks dealt by and to this Pokemon will simply deal damage, never indicating effectiveness or critical hits.

>>32011624
I was thinking Psychic/Dark