In Hades, character progression relies heavily on which gate player picks since clearing each room have their own perks. Because of this its always helpful to know what kind of perk next room will provide before entering it. Luckily, the game utilise symbols on gate to depict this. Each symbol represents a specific kind of perk that the player will be receiving next door. This guide covers all the gate symbols that the player can encounter in the game. Click on the image to expand if they seem too small.

Darkness
Doors marked with a purple crystal-like symbol represents darkness. It is an artifact used to power up Zagreus's abilities at the Mirror of Night.

Chthonic Key
Chthonic Keys are one of several Artifact currencies that allow Zagreus to unlock additional upgrade choices at the Mirror of Night, as well as additional Infernal Arms.

Charon's Obol
Charon's Obol is one of several Artifact currencies that can be used in Charon's shop or at a Well of Charon to purchase various items. Obol's amount resets to zero once you die.

Charon's Shop
A bag with golden mask signify Charon's shop next door. Charon functions as the game's shopkeeper, selling Zagreus various power-ups, healing items, and boons in return for the obols he collects throughout his escape attempt. This naturally means next door doesn't have any mobs.

Centaur's Heart
Centaur Hearts are artifacts found within the underworld which increase Zagreus's current and maximum health by 25 Health when obtained.

NPC Blessings
Doors marked with an exclamatory symbol represents NPC encounter next door. During these meetings, they will offer Zagreus a choice between multiple boosts. There are three possible NPC that player can encounter depending on the region. These three NPC can be encountered in their region exactly once. This also means there will be no mobs next door.

Sisyphus' Blessings
Sisyphus can be encountered exactly once during each escape attempt in Tartarus (first) region. He will offer Zagreus a choice between Health, Darkness or Obols.

Eurydice's Blessings
Eurydice can be found in Asphodel (second) region. If interacted with, she will offer Zagreus a selection of Underworld delicacies designed to boost his Boons.

Ambrosia Delight - Loved by the gods. up to 2 random Boons of yours are upgraded to the next Rarity.
Pom Porridge - An Underworld delicacy; up to 4 random Boons of yours gain +1 Lv.
Refreshing Nectar - A rare and fragrant beverage; the next 3 Boons you find have upgraded Rarity.
Patroclus's Blessings
Patroclus can be found in Elysium (second) region. If interacted with, he can offer three assortments -

Kiss of Styx Premium - Replenish all uses of Death Defiance.
HydraLite Gold - You restore 30% Health when you enter a chamber.
Cyclops Jerky Select - Your Attack deals 40% more damage.
God's Boons
There are the most common type of symbols engraved on the door. There are total nine gods that provide boons to Zagreus. Out of nine, eight have their own symbols which can be identified via looking at door prior to going in, while Chaos God is quite random and can only be seen player enters the room.

There is already a guide which state each god's boon effects.

Boon effects!
A Guide for Hades

By: Holiday
A quick and comprehensive guide to Hades' Boons; their names, effects, numbers, and their respective gods! As of right now, I'd like to say this Guide is fairly complete.

High Grade God's Boons
Players can encounter some doors having glittering god's symbol with a small skull alongside. This means that the next door has armoured mobs (sort of mini-bosses). Also clearing the room will provide the player with higher level boons which can vary between rare to legendary.

Ambrosia
Ambrosia is one of several artifact currencies that are obtained via bounties. It is primarily used as a special gift for those who have deepened bonds with Zagreus. Friends receiving their first Ambrosia from Zagreus will return the favor with a Companion.

Ambrosia can also be used to increase the effectiveness of a Companion, giving it more uses per escape attempt.

Pom of Power
Pom of Power (short for Pomegranate of Power) is an artifact that increases the level of one of your boons on acquisition.

Daedalus Hammer
The hammer symbol represent's an attack upgrade boon from Daedalus. A Daedalus Hammer is an artifact that improves your weapon by upgrading its attacks.

Boss Encounters
In case you encounter a glittering Darkness symbol with a skull means there is a boss fight ahead. Other than darkness, there can be other symbols like glittering Titan Blood, Diamond and Ambrosia which means boss encounters as well.

Gemstone
Gemstones are one of several Artifact currencies that can be found within the Underworld. They can be used to commission upgrades at the House Contractor.

Note: As visible in above screenshot, the gemstone symbol is glittering along with a skull symbol. Note that gemstone will not always look like this. This is just a special encounter with increased mob difficulty and increased reward.

Chaos Mechanic
Chaos Mechanic was introduced in Chaos Update on Jan 2019. In this, Chaos (embodiment of the primordial void) offers boons to Zagreus which, unlike the instant boosts offered by the Olympian gods, trade a debuff for a certain number of encounters in exchange for greater power further down the line.

Chaos can be spotted via going through the Chaos Gates. They appear as gateways in the floor emblazoned with an image of Chaos's eye, which open and begin emitting smoke when the room is cleared. In order to enter health must be sacrificed unless Chaos's keepsake, the Cosmic Egg, is equipped.

Originally posted by Wiki:
Chaos Gates will only begin spawning after 11 completed runs. They cannot appear in shops, in boss rooms, or in the chamber immediately after a boss. Two Chaos Gates will not spawn within 8 chambers of each other. Gates grow less common in each successive area, and are unable to spawn naturally after the sixth chamber of Elysium. However, a Light of Ixion can override the above conditions and cause a Gate to spawn regardless.

Miscellaneous

Reward Boost
As discussed in last section, on some doors you will see glittering symbols accompanied with a small skull symbol. This means that next door have higher difficulty level mobs like armoured mobs, mini-bosses or bosses themselves. However, this also means that rewards from these rooms will be doubled.

Footnote

Edit Log

Added Eurydice and Patroclus in NPC Blessings list.
Since game is still under active development its possible some aspect of this guide may change. I will try my best to keep this up-to-date. Also if you feel there is some error please comment the same stating with some reliable source.

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