After defeating Ophion, deep in Returnal’s Abyssal Scar, you’ll be able to unlock the secret ending – the monster’s carcass will return to its hole on the ocean floor, follow it.
You’ll find a sedan with its headlights on – this is important for later! Walk to the end of the path, and you’ll wake up outside Helios and receive a trophy for completing Act 2. You’ll be in Act 3 – the secret ending – when you wake back up on the surface.
Find the Sunface Fragments
There are six biomes in Returnal – split between Act 1 and Act 2 – each of these biomes has a Sunface Fragment which will give you a key. You need all six keys to unlock the secret ending.
The Sunface Fragments are deep within each biome, and can be difficult to find. Due to the map shifting, we can’t tell you exactly where each Fragment can be found – so you’ll have to make sure you search thoroughly throughout each biome.
Using the Time Travel machine in Helios’ Armory you can return to Act 1, collect the Fragments and then go to Act 2. You won’t drop the Fragments if you die, so you won’t need to complete it all in one run.
Once you’ve collected all six, you can either choose to defeat the final boss again or die.
You must then search for a Solar Fragment per biome. They are usually in special areas that you can only access with the latest tools in the game, like diving or platform spawning by shooting a blue ball . These blue balls are sometimes a bit hidden in the room. The appearance of a room that contains a key is also a bit random, it may take you several tries to find it. Typically, a corpse holding the key is found next to a data cube or other artifact in this special area. Each biome has a unique and very specific location for the Solar Fragment. And he's never behind a locked staff.
Selene will mention that the item is complete – however, it won’t have combined in your inventory. You’ll need to complete the house sequences in order to get the final key. Selene’s house appears in the Overgrown Ruins and the Echoing Ruins.
Once you’ve completed all the sequences you’ll be transported to a throne where you’ll find the Car Key – this is what you need to complete the secret ending.
Return to the Sedan
You’ve got the Car Key, so now it’s time to head back to the Abyssal Scar and defeat Ophion, again. Jump down into the hole and go back to the Sedan we mentioned earlier and use the Car Key on the driver’s side.
Sit back and enjoy Returnal’s final scene.
Additional content by Robin "Raiden" Bouquet.