Does Necrozma's Ultra Form have priority and bypass its speed or does it use Dawn Wing's low 77 base speed?

Question

For those who have Pokemon Ultra Sun and Ultra Moon, does Necrozma's Ultra Burst transformation to its Ultra Form have priority and bypass its speed while transforming or does it use Dusk Mane/Dawn Wing's low 77 base speed? It would really boost Dawn Wings Necrozma in usage and viability if it has priority.

Answer 1

The ultra burst has priority like mega evolution and it gets a speed increase from 77 to 129