It looks like Wood Hammer, but the ghostly aura around it's tail says it's not
The move will more than likely have to be Wood Hammer. The Reason being its because the tail grew in size, and the tail stick looks like it's made out of wood and Mimikyu is able to learn Wood Hammer by move relearner so you might be right.
Probably frustration, if I remember move Frustration get stronger if the Pokemon hate Something, Anime Mimikyu Hates Pikachu a lot so its possible it's Frustration
In ‘Mimikyu Unmasked’ Jessie tells Mimikyu to use Wood Hammer and does the exact same movement.