Galdiator's arrival

After destroying the modified Homing Spider droid, and the droid and demons accompanying it, the same entry port that let out Battle Droids to assist the Homing spider droid let out more demons. But not just any demon. A Gladiator. Doomguy assumed the Gladiator was originally stationed to guard the portal, but after the Homing Spider droid was destroyed, the gladiator went out to face Doomguy with a squad of demons.

Even though the modified Spider Droid was tricker than expected to take down, Doomguy knew he wasn't trapped with these demons. They were trapped with him.