Unlock Everything:
Go to the end credits song and start playing. Do the opposite of everything the game says. Once you nail enough backwards moves, you'll hear the crowd cheering. From there you can quit the song and check out all your new stuff!
Thanks to Revolution Reader wombat_xing!
The sequel to the award winning Hellblade: Senua’s Sacrifice, Senua returns in a brutal journey of survival through the myth and torment of Viking Iceland. Intent on saving those who have fallen victim to the horrors of tyranny, Senua faces a battle of overcoming the darkness within and without.