Even if you change it to one of Giratina avatars, Antasma still has no way of dealing with him having Immortality (Types 1, 7, and 9), Conceptual Manipulation Type 1, intangibility via being ghost type, Dimensional BFR/Sealing him to the Distorted World that can make dream portals useless, and don't get me started on the absurd AP gap (100,000 dream worlds vs Countless universes)