Play as either modern Doom Slayer, or classic Doomguy.
Entrance
Differs depending on the skin.
Doom Slayer: Rises from the sarcophagus.
Classic Doomguy: Teleports in with the green energy effect from the original Doom.
Alt colours:
Doom Slayer: Standard Dark Green, Red (Cacodemon), Brown (Imp), Black (Shotgunner)
Doomguy: Standard Light Green, Blue Chest with lighter blue legs (Mega Armour), White Chest with Red Legs (Revenant), Pink Chest with Yellow Helmet and Blue Legs (Commander Keen)
General
As mentioned the aim is to try to capture the feeling of Doom gameplay and FPS in general. So to achieve this:
Shooting: Lots of ranged attacks with his weapons, obviously. Some that require more precise aiming than others, and there should be viable ranged kill options.
Resources: A large part of FPS gameplay is resource management, with ammo, health, armour, etc. So to capture this, Doomguy has an ammo counter for all his gun attacks, which can be refilled by dealing damage through melee attacks. This also replicates Doom 2016 gameplay where you have to get close to enemies to regain resources. Maybe he should also recover a small amount of ammo from successfully hitting ranged attacks as well to reward good aim, but that might be harder to balance.
Speed: Doomguys ground movement should be fast, as he is in the original games. Like ridiculously fast. Captain Falcon fast.
Fragility: In the original games, Doomguy was fast and had great firepower, but was fairly fragile. So to replicate this, Doomguy should have a bad recovery, sorry to say. With fast movement and powerful attacks he would need to have a weak recovery for balance. Similar to Little Mac in a way but hopefully balanced better.
Standard attacks
Jab: Standard punch, punch, kick. Punches and kicks derived from Doom 2016 Glory kill animations (with no gore though! Smash is for good boys of course).
Forward tilt: Doomguy quickly thrusts a chainsaw in front of him.
Up tilt: Doomguy quickly thrusts the chainsaw upwards.
Down tilt: Kicks his leg out downwards.
Smashes
Side Smash: Super shotgun blast (With ammo). Somewhat slow start-up, medium damage, great knockback, great range for a smash attack. Intended to be Doom Slayers best kill option for close to medium range
Without ammo - Swings his chainsaw out. Less damage and knockback than the super shotgun, but recovers a lot of ammo.
Up smash: Swings Crucible sword in upwards arc. Basically the same as Ganondorfs, but not as strong. Good range, medium knockback, low damage, fast start-up, and requires no ammo.
Down smash: Doomguy swings chainsaw at a low angle from in front of him to behind him. Slow startup with low range and low knockback, but high damage and recovers the most ammo of any single attack.
Specials
Neutral B: Fire equipped weapon. Pretty self-explanatory, each weapon requires ammo. To keep it simple, weapon ammo is generic and pools from the same meter. Each weapons depletes ammo at different rate, and ammo is replenished through melee attacks as mentioned earlier.
Down B: Weapon select - Press to cycle or hold down to bring up a selection wheel, similar to Shulks Monado arts. Weapons available:
Pistol: - Fast start-up, medium fire rate, low damage, low knock back, low ammo cost. Fast projectile. Intended for easily racking up damage at long distances.
Shotgun - Fast start-up, medium damage that drops off at a distance, high knockback/stun at close range, medium ammo cost. Intended to be used at close to medium range to control space or start combos. Becomes less useful than pistol at long ranges.
Chaingun - Long start-up and cooldown as chaingun slows up/speeds down. High damage, medium knockback, with fast projectiles once chaingun is up to speed. Hard to avoid once going, but chews up ammo very very quickly. Intended to be a high risk/high reward sort of option.
Plasma Gun - Fast fire rate with medium damage, that doesn't drop off. No knockback or stun. Relatively slow projectile speed and medium ammo cost. Intended to rack up damage at long range like the pistol, but more damaging and harder to successfully land.
Rocket Launcher - Fast projectile, high damage with no drop-off, high knockback, medium projectile speed, medium start-up, high ammo cost. Doom Slayers best long range kill option. Also a kill option at close range, but you will take a lot of splash damage.
Side B: Grappling Hook. Doomguy shoots out his new shotgun grappling hook from Eternal as a command grab that pulls the enemy towards him. If ammo is available, Doom Slayer immediately shoots the opponent with the shotgun for medium damage, medium knockback. If no ammo is available, then Doom Slayer punches the opponent for low damage, low knockback, and receives some ammo back in return. Can be used as a tether recovery, even without ammo.
Up B: Rocket Jump. The FPS rep has to have a rocket jump! Doom Slayer aims rocket launcher at his feet, shoots, and the explosion rockets him upwards. Works in midair even though there's nothing for the rocket to detonate on. Can be angled slightly left or right after firing. The explosion itself does high damage and knockback to opponents, and Doom Slayer himself does low damage and knockback when in motion. Doom Slayer can also act again after using it.
The downside however, is that he will still take damage from the rocket explosion every time he uses it, though less than the side B version. It also relies on the ammo counter, so you can't use it to recover with no ammo left. If you attempt to use it, Doom Slayer will swing the rocket launcher around like a club to attack, and get a very small midair boost (similar to Yoshi's up B). The idea is to replicate the mechanics of Doom - in the original Doomguy is fragile and heavily relies on resource management, so his recovery reflects this.
Aerials
Aerials with shotgun variants use up ammo, these always do more damage and knockback than the melee variants.
Neutral aerial: Swings chainsaw around him.
Forward aerial: With ammo - Shoots super shotgun with short range of effect in front of him. Without ammo - Throws a knee out forward, similar to Captain falcon but with no strong sweetspot.
Back aerial: Rams the butt of his super shotgun behind him.
Up aerial: With ammo - Shoots super shotgun upwards. Without ammo - Kicks upwards.
Down aerial: With ammo - Shoots super shotgun below him, spikes opponent. Without ammo - Stomps downward, similar to Ganondorfs but a bit faster and weaker, and doesn't spike.
Grabs and throws
Shotgun blast variants of throws have more damage and knockback..
Grab: Doomguy grabs opponent by the throat with right hand. Pummel is repeated punches with his left hand as in the original Doom. Recovers a decent amount of ammo.
Up throw: With ammo - Super shotgun blast upwards. Without ammo - Punches opponent up.
Forward throw: With ammo - Super shotgun blast forward. Without ammo - Kicks opponent forwards
Back throw: With ammo - Super shotgun blast backwards. Without ammo - Knocks opponent backwards with butt of super shotgun
Down throw: Sweeps the opponents leg and punches them into the ground like this glory kill (without the head exploding of course):
https://youtu.be/BWepwS_p5lg?t=17
Final Smash
Doomguy teleports away, and the classic Doom HUD fills the border of the screen with the BFG equipped. A cursor appears that you use to target another player (think Bowser or Snakes Final Smashes) and after a couple seconds the BFG fires its plasma ball. The player that gets hit directly takes massive damage and knockback. Any other player on screen gets hit with secondary green lasers, for high damage but little knockback.
Taunts
Up Taunt: Gives a thumbs-up to the camera, as he did in Doom 2016 with the Terminator reference.
Side Taunt: Brings out the Super Shotgun and reloads it.
Down Taunt: A bunny walks out from behind Doomguys legs, he leans down and pets it.
Misc
Victory Theme: Intermission from Doom 1
Victory animations:
Doom Slayer - Take any of the taunt animations from the multiplayer, but I'd lean towards the heavy metal horns:
https://youtu.be/Y5CT-9ROofQ?t=133
Doomguy - Takes his helmet off and gives his classic grin to the camera.
Stage: Mars Base - Standard Doom looking Mars base, but after a minute or so the main platform gets teleported into Hell. This way they can sneak a hell stage into Smash without ever actually having to call it that.