VIOS

VIOS (Virtual Icon Of Sin), is an AI of demonic origins and the main antagonist of Doom II RPG.

Tactical Analysis
VIOS is, as the name implies, a virtual Icon of Sin. He interacts with Doomguy through corrupted monitors. When accessing these monitors, the player can either allow VIOS to corrupt the monitor's data, or delete it. If the player chooses to delete it, VIOS fights the player. If the player wins the fight, the data is deleted. The fights get harder the further into the game you go, and deleting the data weakens VIOS for the final fight.

Final Fight
The final fight is set up as six terminal fights with VIOS, like the player has been doing throughout the game. Above each terminal is a portal that closes when the VIOS of that terminal is defeated. After defeating VIOS in any of the terminals, the player will be attacked by other demons. After the sixth VIOS is beaten, he is killed in a cutscene.

Trivia

 * During the player's first encounter with VIOS, if you interact with the terminal using a Sentry Bot, VIOS will say "A sentry bot. How quaint. Put it away."
 * Also during this encounter, VIOS flashes onscreen before several demons spawn.
 * The Holy Water Pistol is unusable in all VIOS fights.