Mega Man Zero/Fridge

Fridge Brilliance

 * Zero's decision to kill Weil seems to be spitting on the laws of robotics that were so important to the series. However, his decision is actually in accordance to the obscure Zeroth Law of Robotics which in essence is a threshold law designed to protect the human race from a Complete Monster, as obeying law 1 would cause humanity to be harmed through inaction. Made especially ironic given that Zero was never built with the laws in mind, yet he unwittingly follows the most important law.
 * Also: Zeroth Law.
 * He was also designed and programmed by Dr. Wily, a scientist who probably wouldn't have programmed any of his creations to be three-law compliant. For all his genius, Weil didn't bank on this.

Fridge Horror
Now remember when he said "I am The Devil"? Now consider these: Being one of the good guys at the start? Check. Being envious to one of the good guys that solved them all? Check. Cursing the tool (i.e the Mother Elf) that was previously used for peace, and created an Anti Christ, to wreck chaos, just to spite said good guy? Check. Being banished to "hell" after all he had done? Check. Said good guy sacrificed himself to stop the whole mess? Check. Being a Complete Monster? You already know. Now sum them up, and then you'll think of him as Lucifer, aka the Devil itself.
 * Omega, the Ax Crazy psychopath whose Hate Plague powers and ceaseless thirst for blood that ended up killing 75% of sentient life. The horror kicks in when you realize that Omega was exactly what Dr. Wily intended Zero to be. In fact, given what happens in the whole timeline, actually letting Dr. Wily win seems to be genuinely preferable to just thwarting his plans. As bad as his schemes got, they never went as far as what Sigma or later villains wanted.
 * Remember, Wily became evil because his pride was hurt. Meaning if he won, it would be more or less just to prove he's better than Dr Light. If he won, mankind would probably just have to deal with his ego for a couple decades until Dr Wily dies(he's already quite old.) Compare that with Sigma and Doctor Weil, and you'll be rooting for Dr Wily in no time.
 * Omega is exactly what Zero originally was before he joined X's team and the Maverick Virus jumped to Sigma.
 * Think of the attitudes humanity has towards genuinely non-violent robots: in MM 9 we see In MMX 6, Gate's Reploids are killed off due to their potential risks instead of merely reassigned; in the context of this series, robots are basically sentient, so humans are willing to leave living people to basically starve to death, or outright kill them, out of convenience. Yet, people like Dr. Wily and Weil get to live, with no "kill on sight" orders established before being captured. How horrifically skewed are humanity's priorities towards robots and humans to even allow this to happen? The worst part about this? This means that Dr Weil's Hannibal Lecture has ground. Only humans understand the joy of power, indeed.
 * This goes double when you read Mega Man Zero Official Complete Works; his reason for starting the Elf Wars was that he thought Reploids were getting off too easy for the massive destruction caused in the Maverick Wars, especially once the plan to solve the Maverick problem was to basically install anti-virus software and call things even. On the surface it makes sense; each X series game chronologically takes place a few months after the last one, meaning not even half a decade had passed since Reploids were made before Sigma caused multiple wars and a Colony Drop. And similar to how Weil fails to grasps his exile was his own fault, the wars were humanity's fault for making Reploids so powerful in the first place.
 * All of them makes Weil even more terrifying. How? Because it means he had a good reason behind his Fantastic Racism. The Complete Monster had JUSTIFICATION.
 * Weil's "warning shot" with the Ragnarok was the only reason Zero & co. were able to defeat him. If Weil had just kept his mouth shut and improved his aim (which he had plenty of time for since he was presumed dead from the destruction of Neo Arcadia), he could have used that shot to annihilate Area Zero or the Resistance base where Zero and Ciel were at the time. That's right, if it weren't for the Villain Ball, Weil would have won, right then, right there, with nothing you could do about it.
 * From the manual: Weil was among the scientists who tried to resolve the Maverick Wars; specifically, he and his colleagues studied Zero's empty body. However, while Ciel's ancestor studied Zero's cognitive program for a cure, Dr. Weil viewed Zero's body as the ideal weapon to end the wars and used it develop Omega, while Ciel's ancestor created the Mother Elf, which would be used by the original X to purge the Sigma Virus for good. Dr. Weil then proposed Project Elpizo, a plan to combine the Mother Elf with Omega to exert control over all Reploids. This put Dr. Weil at odds with X's ideals of coexistence between humans and Reploids. Undeterred, Dr. Weil placed a "curse" on the Mother Elf that turned her into the Dark Elf, and created clones named Baby Elves to control Reploids and make them fight eachother in a massive battle royale. The panic and destruction caused the people to favor Project Elpizo, but X and Zero (whose program was put in a new body) recaptured the Dark Elf, forcing Dr. Weil to unleash Omega in the battlefield. Omega would move on to slay a large number of humans and Reploids before being finally defeated by X and Zero. Omega was sent away to Earth's orbit in the Forbidden Ark, while a group of humans converted Dr. Weil into a cyborg and cursed him to wander the wastelands of Earth as punishment for his crimes.