To protect his fellow mutants from human/Sentinel hybrids, Magneto turned a paper clip into a deadly weapon. In the Magneto (2014) miniseries at Marvel Comics, the Master of Magnetism sought answers from those threatening mutantkind. To stop the destruction and deaths of his fellow mutants, Magneto brutally murdered a scientist in a scene that's far too gruesome to ever appear in the Marvel Cinematic Universe.
Magneto is responsible for some very dark moments in the pages of Marvel Comics. He's used his powers to kill many of his adversaries, including murdering his son Quicksilver by crushing him with a Sentinel. His death led to House of M. Magneto has been particularly brutal against Wolverine as he's ripped the adamantium right off of his skeleton. He took things a step further in the Ultimate Universe, as Magneto killed Wolverine by melting him with his fellow Avengers' weapons and stripping his skeleton bear. However, one of Magneto's simpler kills is among his darkest ever.
In Magneto #3 by Cullen Bunn, Gabriel Hernandez Walta, Jordie Bellaire, and VC's Cory Petit, Magneto broke into a facility where homegrown Sentinel/human hybrids were created to murder the X-Men. After making his way through defenses, Magneto runs into the project leader of the experiments. When she refuses to help him destroy the Sentinels, Magneto tells her she will and shows her paper clips. He controls the clips to enter her through her arm, causing the doctor significant discomfort.
The doctor reveals to Magneto all of the mutant deaths were "oversights" and that the Sentinels were designed to defend against their attacks. She tells Magneto she won't help him, even if mistakes were made along the way. Magneto doesn't waste any time sending the paperclip throughout her body and rip apart her insides with the small metal object. The doctor dies as the paper clip slices her neck. Magneto subsequently detonates the facility, as well as a decommissioned Master Mold.
The comic showed how powerful Magneto truly is, even with a weapon as small as a paper clip. He used his powers to send the clip into the doctor's arm and destroyed her body from within when she wouldn't cooperate with him. It's quite a disturbing death, as the doctor can only react as the paperclip slices her throat from the inside. While it's a memorable moment for the mutant in the comics, the scene is almost certainly too disturbing to ever appear in the MCU whenever the X-Men finally get introduced, even if it perfectly emphasizes just how incredible Magneto's powers are.