>>35818539The "1000 arms" are actually a property of Bodhisattva Avalokitasvara (Kannon), a Buddhist deity. The 1000 arms symbolize their ability to who can travel between worlds, meaning its transcendence of time and space.
The golden "crown" around Arceus's body also looks like the spiky aura this bodhisattva is usually represented with in statues.