I've made a new challenge in Below Zero using the Custom Gamemode. Here are the settings:
Hunger: on
Thirst: on
Everything else untill Permanent Death: on
Story: on
Initial Equpment Pack: I suggest having it on, since it makes everything just a tiny bit more bearable, but ditch everything but the Scanner, Knife, Fins, and Mobile Vehicle Bay
Allow Permanent Death: I suggest OFF, because all the stuff that can hurt you, one hit's you, even with the Reinforced Dive suit. Except Symbiote.
Alerts: off
Organic Oxygen Soruces: Doesn't matter either way, only matters early game.
Weather Effects: on
Vegetarian Diet: on
Day Length: 0:05
Night Length: 0:15
Bad Weather Frequency Multiplier: 4
Player Damage Taken: 10
Vehicle Damage Taken: 10
Preadator damage taken: 0.05 or 0
Creature Aggresion: 10
Hostile Creature Spawn: 1
Peaceful Creature Spawn: 0.01
PREPARE FOR MISERY