Relics are a kind of reward for doing challenges in the game. There are side rooms that have a specific challenge to them.
This is what a Relic room looks like.

So far, I've ran into "No Jump Pack" and "Who Turned Out the Lights?". They are pretty self explanatory.
"No Jump Pack"- Only jumping, no booster.
"Who Turned Out the Lights?"- Only lights from your jumper, your gun, and any environmental source of light has light, otherwise the room is dark.
I've also ran into rooms that give you no special information about them. These are just parkour rooms.

From these rooms, you can collect Relics. Relics give you bonus rewards/stats/affects for completing the room and opening the chest. From these chests, you can get any number of Relics that each have specific characteristics to them.
Relics are also scattered around the normal play area sometimes. I've found a couple of them in the normal play area.
When you open a Relic box.

When you hit ESC, they will appear in the pause menu looking like this.
Relics can stack. What does this mean? More than likely increases the reward or resistance of whatever that relic is. I have gotten up to three of one item.

You can see I've gotten a lot of Relics in this run.


I will add to this list as I find more relics. I will also try and get images for all the relics.

Fire Resist- Increases resistance to fire damage.

Gas Resist- Increases resistance to poison damage.

Resit Death- Gives you a chance to resist a fatal shot.

Health Regeneration- Regenerates health over time.

Faster Overheat Recovery- When you overheat a weapon, the cooldown for when you can reuse the weapon is shortened.

Overheat Capacity+- Increases how much you can shoot before your weapon overheats.

Plamsa Resist- Increases resistance to alien shots.

Knockback Immunity- Reduces the distance at which you can be knocked back.

Melee Resist+- Increases resistance to melee damage.

Shorter Utility Cooldown- Reduces the amount of time before you can reuse equipment.

Backpack Health Restored- Instantly restores health of the backpack to 100%.

Earn More Goo- Increases amount of goo dropped from enemies.

Faster Respawns- Decreases the amount of time it takes to respawn.

Acid Resist- Increases resistance to acid damage.

Threat Reduced- Reduces the time at which enemies will notice you.

Longer Flight- Increases amount of jetpack.

More Dark Levels- Increases the chance of you getting a dark level.

Faster Movement- Increases movement speed.

Impale Damage Down- Reduces damage done by spikes.

Cold Resist+- Increases resistance to cold damage.

Electric Resist+- Increases resistance to electric damage.