(This is my first time doing a Death Battle so i hope i do a good job at doing this, i don't own these two games or the characters although it would be awesome if i did. Since no one ever thought of adding this or think that this fight is not really good so I'll make my own showdown between the two, if you don't like it then go to hell.)

Two legends clash in an arena and only one will walk out of there alive, a fight between two powerful foes that will clash against each other and give everything they got at one another. The deadliest demon will stand at the top of the hill waiting for his opponent to arrive on the field, he will arrive all armed and ready for a fight as he has slaughtered so many demons there is only one demon that stands before him, thinking of him as the Icon of Sins and of all demons he has killed he has never went one on one against this great demon of hell.

The greatest demon of all time Vs the greatest demon slayer of all time.

DOOM:

Titles: Doom Slayer/Space Marine/Doomguy/Hell Walker/Unchained Warrior/Scourge of Hell

Relative: He is related to the Grandfather of Shooters (Wolfenstein) and is related to another shooter game that changed the world (Quake)

His story: He was the most feared person to walk all over hell killing thousands or maybe millions of demons in the past, destroying everything that stands in his way, his alignment is the Night Sentinels probably an order that takes on the demon hordes and only he can save the human race by destroying all the demons again on Mars, no demon can never face him however they manage to seal him away in a tomb but he was brought back when the UAC found him and now he is back to raise some hell once again.

(Those abilities i got them from the Wiki so i don't own that all credits goes to whoever wrote them down, if it's a problem then I'll remove them and rewrite them.)

Abilities:Superhuman Abilities: The Doom Marine possesses powerful superhuman abilities, which are all used when the Marine is fighting against Hell's Legions. His superhuman Strength means he can rip, tear, and crush Demons and Cyborg's with relative ease, which the Doom Marine uses to take down even the most powerful of Hell's minions. His Endurance, Stamina and Durability gives The Marine the ability to take large amounts of damage without stopping (Though he can still die from natural causes such as high falls, and isn't able to survive death hits when his health is at zero). The Doom Marine is also extremely fast, mobile and agile, allowing him to traverse and maneuver around the environment and battle arenas whilst also battling Demons and dodging attacks. The Doom Marines greatest superhuman feats are shown when he kills the towering Cyberdemon by tearing out its Argent accumulator and then using its horn to decapitate it after it revived, defeating the highly durable Hell Guard by killing the parasitic controllers inside of them (Used first Hell Guards own weapon to stab through its armor and kill the parasite from within, punched through second Hell Guards armor plating and squished its parasite, and killed the third Hell Guard by ripping off its armor before tearing the parasite in half), and taking down the powerful Spider Mastermind.

Though it is only told by demonic recordings, the Doom Marine had managed to kill Hell's greatest Champion 'The Titan', indicating how powerful he is and how he became the most feared being to Hell's Legions.

Argent Energy Absorption: The Doom Marine can absorb Argent Energy via his Praetor Suit, which reroutes it throughout the suits subsystems and into his body. This allows him to increase either his Health, Armor or Ammo to maximum levels.

Rune Absorption and Usage: Through some unknown means, the Doom Marine is able to use mystic runes that he gains upon completing trials. Once a trial is complete, the Marine can then equip a rune to gain new abilities.

Master Combatant and Weapon Mastery: The Doom Marine is capable of utilizing any weapon or firearm in his possession with expert handling. He can use all firearms he comes across with great effect, while also upgrading and modifying his arsenal. He is also capable of carrying a vast amount of weapons, carrying up to 12 weapons including special weapons and grenades. When performing a glory kill, the Doom Marine uses a unique fighting style that allows him to quickly but brutally, rip and tear demons apart in a short amount of time when in a very close vicinity.

Weapons: Handgun/Combat Shotgun/Chainsaw/Chaingun/Assault Rifle/Super Shotgun/Plasma Rifle/Gauss Cannon/Rocket Launcher and finally his greatest weapon in maybe video game history is the BFG9000

His opponent...

Diablo:

Titles: The Dark Lord/Lord of Terror/The Prime Evil/Dialon, Spirit of Determination/Survivor of the Dark Exile/Leader of the Three/Destroyer of Souls/The Terror Lord

Relatives: Mephisto and Baal (Brothers) Leah (Daughter) Lucion (Nephew) Lilith (Niece) Rathma (Grandnephew)

His story: Diablo spawned from one of the seven heads of Tathamet; his domain in the burning hells was the realm of terror. Diablo took part of the Eternal Conflict and the others didn't really worked together in the fight, just as they were close to a win Diablo turned on them determined to be the sole ruler of heaven and hell. He has fought many battles and continues releasing his demon spawns to the world, he is a very powerful immortal being and when he is killed he will always return there is always a way for him to return back and bring the apocalypse yet again, being as the only prime evil to walk hell.

Abilities: Slash: a rapid melee strike with Diablo's hoof, claw, arm blade or tail, dealing average Physical damage.

Fireball: a ground-based missile that, upon reaching any target or obstacle, explodes into a pool of fire, doing high Fire damage over time if you're caught in it.

Flame Circle (similar to Diablo II equivalent): creates a circle of ground-based fireballs, each doing average Fire damage, moving in all directions. These do not leave a pool of fire.

Fire Wall: creates a fast-moving wall of fireballs, similar to Flame Circle, but with an arc and moving faster and further. Deals same damage as Flame Circle.

Bone Prison: creates a series of black pools on the ground, trying to create them as close to the player as possible. If caught in it, Diablo will teleport to you, grab you by the throat and drain your health before slamming you into the floor. This attack cannot actually kill a hero (reducing to 1 Life instead), but is often followed by a Slash. Some defensive abilities can be used while grabbed. Note that Bone Prison stuns the character instead of immobilizing them, so Teleporting out will not be possible.

Teleport: used both to get closer to ranged characters and to avoid melee combat. Used automatically if player gets caught into the Bone Prison.

The Realm of Terror: after suffering enough damage (about 65%), Diablo stuns you and shunts you off to his Realm of Terror, essentially a dark and shadowy world, but without Healing Wells. Here, you will need to fight two major enemies.

Shadow of Diablo: has roughly half the total health of Diablo in phase 1, uses all the same tactics of Diablo during the first phase and should be fought the same way. However, from time to time he disappears, spawning a number of Shadow Clones equal to the number of players in game. After 30 seconds or once the Shadow Clone is dead, Shadow of Diablo will return.

Both of them will take place in the same area where the Doom Slayer fought the Cyberdemon, in this large wide area in the UAC. The Lazarus Lab is perfect for a wide fight between both the deadliest demon and the deadliest slayer, both are armed at the ready and there is no way out because the only way out is if one of them lies dead on the ground, will the deadliest prime evil defeat the Doom Slayer or will the Doom Slayer annihilate this beast and walk out of there, looking for another challenge.