Sentinel crystal

Sentinel crystals are a collectible item found in Doom Eternal, replacing the Argent cells from Doom (2016). Found inside small blue shrines, each crystal that the Doom Slayer finds allows him to increase either his maximum health, armor or ammo capacity as desired - each stat can be upgraded four times, therefore there are twelve crystals in all to locate.

The first crystal is found in the Fortress of Doom after completing Hell on Earth and must be taken to advance the game; the remaining crystals can then be found off the beaten path in subsequent levels (two further crystals are stored in the Fortress and require two Sentinel batteries each to acquire). On selecting an upgrade, the Slayer breaks the shrine open with a punch before taking the crystal inside it.

Boosts
Each health upgrade increases maximum health by 25 points, from a base capacity of 100 up to a maximum of 200. Each armor upgrade increases maximum armor by 25 points, from a base capacity of 50 up to a maximum of 150.

Each ammo upgrade increases the maximum ammo capacity for all standard weapons by a linear amount. Argent cells and the chainsaw are not affected; players can only ever hold a maximum of 60 Argent ammo and three units of chainsaw fuel at a time.

Linked bonuses
As well as the direct boosts, there are six further bonuses that can be unlocked by purchasing both upgrades linked to a particular bonus.
 * Quickdraw Belch - Flame belch takes less time to cooldown.
 * Loot Magnet - resource drops get pulled in from much further away.
 * Napalm Belch - heavy and super heavy demons stay on fire longer.
 * Health for Blood - when at maximum health, all health pickups are used to recharge the blood punch
 * Belch Armor Boost - demons drop armor shards at a faster rate
 * Armor for Blood - when at maximum armor, all armor pickups are used to recharge the blood punch

Using the first crystal completes the "Crystal Craving" milestone, and fully upgrading either health, armor or ammo will complete the "King of the Crystals" milestone. Conversely, completing the game with only one crystal and one Praetor suit perk will complete the "Can't Perfect Perfection" milestone.

Crystals do not appear in Part One and Part Two of The Ancient Gods; players start with all crystal upgrades already unlocked.

Trivia

 * The Wraith's Crystal used to power the Gate of Divum in Part Two looks identical to a Sentinel crystal.