The Gladiator

The Gladiator is a demon that debuted in Doom Eternal. It serves as the boss of Sentinel Prime.

Codex Entry
"In the years following the end of the Golden Age, competing factions of Argent D'Nur turned against one another. An insidious influence has set itself upon the Sentinel people, corrupting its once sacred traditions. The coliseum, once a place of honorable combat where prisoners of the Argenta were tested for the right to fight in the front lines of their army, has since become a place of blood-sport. In violation of Sentinel law, the Priests have encaged a demon there, a merciless executioner used to enact judgement of their own decree. The Gladiator, wielding an accursed shield which entombs the tormented soul of his undying master, remains undefeated in battle, infamous for the many lives it has claimed."

Appearance
The Gladiator has a large body similar to the sketch of the classic Hell Knight by Adrian Carmack, but with the addition of some body armor. Its head resembles a classic Hell Knight, but missing one of its eyes. It wields a shield and mace for weapons, changing to a pair of maces once its shield is destroyed.

In The Art Of Doom Eternal, it's stated that the Gladiator is capable of resurrecting itself as long as its shield (which contains the soul of its unidentified "master") remains intact. The body will simply re-form over time and the creature's soul will return to it. The face on the shield somewhat resembles that of an Archvile.

Combat Characteristics
The Gladiator hides behind its shield to shrug off attacks, and has two main attacks: a lunging slam cued by the shield's eyes flashing green and the same sound cue as the Marauder's axe swing, and a projectile fired from the shield cued by the face twitching its mouth. Any high amount of damage such as a close range Super Shotgun blast or a headshot just as the former attack is beginning will stagger the creature and place it in a state similar to a Glory Kill: performing this will deal a set amount of damage and cause the Gladiator to drop health.

Once the creature's first health bar is depleted it will lose its shield and draw a second mace. In this state it is more mobile and gains an ability to reflect damage by twirling one mace. There are a few distinct attacks related to the twirling mace move: It retains its slam attack along with a long-distance rush, more mace swings including a long-range swing, and an attack similar to the 2016 Cyberdemon where it forms a "corridor" between two energy walls and sends wavy energy lines towards the Slayer: these have "up" and "down" sections and it is necessary to anticipate their motion to determine safe spots. Once done with this attack, it will swiftly lunge into the Slayer's direction, but can be put into a stagger state with a well timed shot. These factors, along with its ability to deal massive damage, makes the Gladiator a formidable foe, and a potential roadblock during an Ultra-Nightmare run.

First Phase
When The Gladiators eyes flash green, It can be stunned with significant burst damage. The most reliable strategy for dealing maximum damage during this stunned state Is as follows. Stun the creature with the Super Shotgun, follow up with a ballista shot, a Precision Bolt headshot, then another Shotgun blast and ballista shot, finished with the glory kill. You should launch two grenades If you have them during this time as well.

The combo simplified would then go: shotgun - (grenade) - ballista - headshot - shotgun - (grenade ) - ballista - [glory kill]. Omitting the grenades can save a lot of mental strain on this combo, and It Is still highly effective without them, don't be afraid to forgo their use If it Is too hard to pull off to start. Overall this combo seems to be the easiest and most effective strategy to pull off during the first phase, and will bring The Gladiators health bar down very fast, using this strategy as well as the Chainguns Energy Shield should make the first phase extremely easy once practiced.

Utilizing the Meat Hook to jump over The Gladiator to get an easy, relatively low risk close range shot is also effective. This can be followed up with a ballista shot directly downward onto The Gladiator to deal more damage and increase air time. Allowing you to combo more free damage. This Is very good to use during downtime on the Chaingun Energy Shield.

Second Phase
The second phase is much harder than the first, and The Gladiator has more dangerous attacks that must be dealt with, or else you will die very quickly. The most important attacks to pay attention to are the ones where the creature swings its flail. These can be broken down Into 3 distinct and important types: The Swinging Strafe, The Swinging Stampede, and The Jumping Flail.

The Swinging Strafe Attack starts when The Gladiator swings their flail and starts moving to the left or right of the arena, they will also back away from you slowly, this attack is led with an eye flash, so It's Important to close distance on the gladiator and be prepared to stun and damage them. The same combo as phase one should be used to great effect.

The Swinging Stampede Attack Is similar to the strafe attack, however, The Gladiator will advance on you rapidly, this attack hardly ever has an eye flash prompt to stun, so you should back away as best as you can while holding out the Chainguns Energy Shield to counter this attack.

The Jumping Flail, commonly referred to as the  jump rope attack, Is led with The Gladiator moving towards the center of the arena while swinging It's flail, or If they are already there, they will just stay In the center. During this attack you have to do your best to dodge the energy waves that come toward you. At the end of this section, The Gladiators eyes will flash green, and they will immediately begin a charge attack. The window of opportunity to stun the beast Is extremely unforgiving, and missing your chance even slightly will allow The Gladiator to charge close enough to do massive damage. The key to trivializing this encounter is to stand as far back from the center as you can. Which will give you the most time to react to the energy waves, as well as time to react to the charge attack. The only way to reliably stun The Gladiator from long distance Is with a Precision Bolt placed anywhere on It's body, although a headshot Is preferable. If you can get the timing down, you will hardly ever have to worry about this attack and It will become free damage more often than not.

Any time The Gladiator Is not swinging their flails, they are throwing them at you, the best way to deal with this Is to equip the chrono-strike rune, and to use the Chaingun Energy Shield as much as possible. Any time the shield Is depleted It's best to Meat Hook jump over the beast, and combo It with the Ballista for more damage / airtime, and Precision bolt Headshots from above.

The Gladiator always starts the second phase with the Swinging Strafe attack, and after the second flail swing based attack they will always spawn a prowler, two gargoyles, and a zombie. The Gladiator also has an alternative of this pattern where they will spawn a prowler, two soldiers, and a zombie intermittently throughout the fight. This can be extremely useful for using an ice bomb or blood punch to chainsaw combo to replenish resources while or immediately after the gladiator has been stunned.

It Is worth note that unless The Gladiator has received enough damage between swinging flail based attacks, It will be very unlikely for them to initiate another. It's important to always shoot the gladiator, or you risk prolonging the fight for longer than necessary.

Trivia

 * The Gladiator's face and body bears a strong resemblance to the Barons of Hell and Hell Knights from the classic Doom games. It's a beefy faun like them, as opposed to the more ogre-like Hell Knight in the 2016 game or Doom Eternal.
 * The Gladiator's design appears to be based on the Secutor Gladiator, who fought with a heavy shield and a sword/dagger.