She-Ra: Princess of Power (1985)

S01E57 Jungle Fever

Adora gets seized and hauled to Beast Island, where she breaks out of her cell—only to smack her head and wake up with no memory of who she is. Stranded and confused, she stumbles into a rugged tribe of Beast Warriors living by primal rules. To survive, she must prove herself against the terrifying Great Beast that rules the island.