Researcher Matthews was not having a good day. First, it was his alarm going off 10 minutes late, forcing him to rush his carefully prepared morning habits. Then, his car had refused to start, meaning he had to carpool with Assistant Researcher Anders, who proceeded to talk his ear off for the 35 minutes it took to arrive at Site-64's motor pool, pausing only to acknowledge the checkpoint guards along the way. Matthews was looking forward to some nice, fresh coffee, but it turned out that all the good stuff was gone. He grumpily accepted some tea instead and went to his office in the Anomalous Research Division.
That's where he found the splattered remains of Chief Researcher Nasan, and decided that this day could go fu-
"Mr. Matthews?"
Roused from his fuming contemplation, Matthews looked up at the security officer in front of him. "Look, Officer…" He squinted at her name tag. "…Bradford, I've told you everything I know, which isn't much. If you don't mind, I'd like to go back to work now."
Instead of a response, he was handed a note. The woman gestured toward the body, wordlessly explaining where she had gotten it from. Sighing heavily, he plucked the note from her hand and took a look.

the mermaid made me do it xoxo Bag Man

The cogs of Matthews' mind began turning at the word "mermaid". There were hundreds of anomalous items within the Site, and not all of them had been properly documented. Still, a mermaid of all things would've stuck out a bit more than the others.
A sudden rapport of gunfire out in the hallway diverted his attention away from that mystery, especially when the door was launched off its hinges at an unbelievable speed. Bradford drew her sidearm and waited for someone to enter the room. A tense silence hung in the air as the gunfire ceased.
Matthews was still looking at the door when she started firing. Whipping his head around, he caught a glimpse of… a brown paper bag? Maniacal laughter filled the air as Bradford lowered her gun, a confused expression plastered on her face. She turned to him, and he noticed for the first time that her mouth didn't move when she "spoke".
"My shots just flattened against whatever he was wearing. Are there any anomalous items here that are bulletproof?" Matthews noticed the strange, monotone patterns in her "speech", and realized that she was using a rudimentary form of telepathy. Just another day in the office, I suppose. He shook his head and walked over to the doorway.
"I'm afraid I only just started here two weeks ago. I haven't been able to memorize everything-" He paused when he felt something squish under his shoe. A slow, agonizing dread crept into his heart as he reached down to pick up the object in question: a rubber band. Pained realization wormed its way into his mind as one of the few items he had memorized leapt into his thoughts:

Item Description: A wooden toy rifle designed to shoot rubber bands using a gear. Rubber bands accelerate to 1/540 the speed of light upon leaving the barrel of the rifle.

When he had first heard about that particular item, Matthews had converted the speed into miles per second: 344 mps. In other words, anything hit by a projectile coming from that gun wouldn't be doing so well after the impact. If some madman had gotten his hands on that thing…
Fortunately, he knew exactly what to do.
"You didn't happen to find a knife on Nasan's body, did you?"

Site-64 had devolved into chaos, as Bag Man ran wild throughout it. Walls were blasted down, security personnel were shot and looted (ignoring the clearly inferior weapons), and everyone else either ran or cowered from him. Shots simply pinged off of his freshly "borrowed"1 body armor, and failed to penetrate his anomalously impervious head bag.
Occasionally, he would shout at those in his way with phrases such as "YOU'LL COWARDS DON'T EVEN SMOKE CRACK!", "YOUR RESISTANCE ONLY MAKES ME HARDER!", and "FREE WILL IS A LIE BECAUSE NONE OF US CHOSE TO BE BORN!". Responses ranged from horrified screaming to futile attempts to subdue him. He didn't really pay much attention to the respondents, seeing as they all died in the end.
Originally, he had planned to steal more from the Site, but things heated up far too quickly for his liking. After all, even crazy people have a sense of self-preservation. Still, he would make sure that no one forget his name: Bag Man!
The janitor he was explaining all this to was, sadly, in the process of dying from a heart attack, desperately trying to reach for the aspirin Bag Man held in his hand.
"Man, it feels GREAT to get all that off my chest! Thanks for listening, dude!" He tossed the bottle next to the man's head, and watched him swallow the pills, shooting him when he was finished.
"NOTHING PERSONAL, KID!"

Matthews and Bradford ran towards the motor pool, following the carnage left in the wake of Bag Man's insanity.
"When we catch up to him, Bradford, I'll need you to distract him so I can get up close and stab him!", Matthews shouted over the alarm blaring through the Site. Bradford nodded, pulling out her pistol as they entered the motor pool.
Aside from the constant alarm, silence hung in the air as they slowly swept through the area, hoping that the Bag Man hadn't escaped. Matthews quickly checked to make sure the knife was still in its sheath, remembering its description perfectly:

Item Description: A combat knife with a serrated blade and a wooden handle. Whenever this knife is used with the intention of harm the knife blade will disappear through unknown means. This event is un-observable and happens instantaneously. When in this anomalous state any person(s) "stabbed" with the knife will instantaneously and unavoidably whisper the phrase "I'm dead" and lie down. After about 4 minutes the victim will reawaken unharmed with no recollection of the event.

Right as they reached the exit checkpoint, Matthews stopped. The sound of a small electric motor drifted into the air, and dread crept into his heart once more. Slowly turning around, he saw the Bag Man on a moped, barreling towards them and the exit.
"GET DOWN!", Matthews yelled out, diving to one side of the exit. Bradford complied, taking the other side. As she leveled her gun at the moped…
"NOT TODAY, COPPERS!"
The Bag Man pulled out the toy rifle and fired at her, all in an impossibly fast motion (and while maintaining control of the moped). The shot failed to hit her directly, but the resulting shock-wave knocked her off her feet and into a wall. Bag Man's maniacal laugh petered out as he scooted away, two more blasts signalling the destruction of the remaining checkpoints.
Matthews ran over to Bradford, quickly checking for a pulse. Blood leaked from her ears and mouth, but there was still a heartbeat, albeit a shaky one. Coughing signaled her return to consciousness, more blood spilling out as she did so. After a few pained breaths, Matthews felt her telepathy kick in:
"w̸̴̷͘è̀̕̕͢ ̕n̸̕͘e̵̢̢e̛̕d̡͏̛̀ ̀̕͢͝t̶͜o̵͏ ̢́͝͠f̡͜͝i̴̕͜͝ń̕͜͢d͘͟͠ ̵̡̀͘͝h̷͝͠͏į̧́m͟͝ " He winced as the message painfully cut into his brain.
"You're clearly in no condition to go anywhere right now, except for an infirmary. Why don't I just call for backup…" He paused, quickly checking his pockets for his phone. After a brief moment, he realized that he had left it back home. The adrenaline built over the last ten minutes finally wore off, and he slumped to the ground next to Bradford, defeated.
He was officially having a terrible day.

Footnotes
1. Read: stolen.