Angry and malicious in behavior, like the Doom Slayer before him, he is just [an Absol/a Rabbit] too angry to die. There is a reason he is called the [Mobian: EXE Slayer/Pokemon: Doom Absol].

Personality and Attitude:
His personality is predefined, showing little to no emotion. Anger, Hatred,and Violence are the main things that shape Roy's Doomguy-inspired nature. Despite this, he shows a heart sometimes, his dead [Rabbit/Victini] friend might've been the sign of his whole kindness only for that to disappear when his friend was killed.

Powers and abilities/moves:

(Note: Pokemon variation contains fake moves)

Mobian variation only:

Roy Knight's homing attack has an explosive vicinity, any targets near him will be destroyed, armored targets effectively lose their armor with one shot. It works effectively greater when he wield a chainsaw.

Roy's spin attack is also different in terms of executing it. Most spin attacks are in a shape of a rolling ball, his spin attack is more of a literal spinning top. Roy can also shoot his guns and use his chainsaw or his crucible whilst spinning.

Both:

The way Roy dodges, and strafes is very similar how a player moves; choosing to shoot at a distance and when getting close he suddenly unleashes a devastating close range shotgun blast or a chainsaw.

Argent Blast : Basically a mini version of the Lazarus Wave. Targets near the glowing red Roy that will release a red colored shockwave, burning targets to the bone. Those affected by the blast will turn into Possessed, 3-4 Imps and 1 Pinky will spawn inside the blast. A rare sight if it spawns a Baron of Hell.
The Argent Blast is a one time use.

Pokemon variation only:

Argent Pulse (Pokemon only): Roy unleashes an orb filled with terrifying and satanic thoughts. Target will be inflicted with low damage and but also has 45% of flinching a target

Blood claw (Pokemon only): Works the same to damage dealing moves which has an increased critical hit ratio, target's defense decreases by 10%.

Argent Slash (Pokemon only): Works like Blood Claw, but instead of decreasing the target's speed, it gives them a burn status. He stuns targets for 6 seconds but this only works for Ghost Pokemon. Roy's PP will decrease upon 50%.

(Argent Slash idea came from my friend's classmate)
(The idea of Roy's unique spin attack is my idea when I was tired of seeing many people using the rolling ball style of the Spin Attack of their Sonic OCs)

Doom belongs to ID Software
Sonic belongs SEGA
Pokemon belongs to Nintendo and Game Freak