Asriel on 11 June 2019
That is 100% Ganon's corpse. The hand holding it down is some kind of Sheikah magic sealing the corpse beneath the earth. My guess is what we're seeing is the very start of the game - Zelda and Link travel beneath the castle to find and destroy Ganon's corpse, but things go wrong. Ganon breaks free and retakes his human form (which has presumably been sealed for millenia given what we learn in BotW).
