How to get the secret ending in High On Life

 How to unlock the secret ending and find an easter egg hinting at a continuation of the game

To unlock the secret ending, you must defeat Nipulon, who is associated with the penultimate contract in the game. Once you've done that (or even killed the Garmanthus), go back to the teleporter and choose the second option. After that, select Nova Sanctus and go to Clagg's office. Once in his office, go to the table and take the card key located next to his computer.

Once you have the card key, return to the teleporter in the house and go to the human harbor in the Unknown Sector. Once you get there, look up and jump across the platforms from above. To get to higher levels, you need to use a jetpack. Soon you will reach a platform with a red light and a closed door. When this happens, look up to see a flashing red light. Use the jetpack to fly toward the light.

Once you get to the top, follow the path until you find a door with a No Entry sign. You need to use the keycard you received earlier to open this door. When you enter the room, get the Sequel-Bait achievement. Use Sweezy's ult to go through the vents ahead. Keep following the main path; eventually, you will reach the scientist. When he finishes talking, Kenny will joke about having to wait until the next one to see what happens. When you leave the room, you will see Klagg's workers waiting for you outside. They will say that they will do everything they can to help you and humanity. Once the conversation is over, you can leave the human harbor and return home.