Reed Richards, AKA Mr. Fantastic, is one of the smartest people within the entire Marvel comic universe. He has invented many incredible inventions throughout his time leading the Fantastic Four, but those inventions sometimes have a tendency to bring about dangerous situations because of the power they hold.
With the announcement of the Fantastic Four coming to the MCU, here are the 10 most powerful inventions of Reed Richards.
10 The "Solve Everything" Plan
The Reed Richards of Earth-8155 has literally solved every problem that reality has. The "Solve Everything" Plan has put an end to hunger, diseases, wars, and literally every other problem the world faces. While not particularly a powerful creation, it just shows the kind of inventions Mister Fantastic can come up with if he puts his mind to it.
9 Coma Cannon
Reed and Sue Richard's son Franklin is a mutant who has incredible powers that essentially make him a god. He can change reality itself, essentially being able to do whatever it is his child mind wants. He has revived Galactus, defeated Mephisto, the Marvel version of Satan, twice, and has created his own universe while playing in his room.
Needless to say, having that kind of power as a kid is a very dangerous situation which led Mister Fantastic to invent the Coma Cannon. He uses it to put Franklin into a coma while the kid is having a nightmare. Fatherly love at its finest.
8 The Bridge
The Bridge is a device that allows Reed Richards to look into different realities. He uses it to assemble the Council of Reeds, which is a group of the most accomplished and brightest Reed Richards throughout the multiverse.
During the events of the Incursion, he uses the Bridge to look into other realities to see how other Earth's handle the multiverse Earth's colliding into each other to try to find a way to prevent it happening to his Earth.
In Fantastic Four #73, Daredevil is racing to the Fantastic Four to inform them of Doctor Doom's newest evil plot. When he arrives though, Mister Fantastic, Human Torch, and the Thing believe he is actually Doctor Doom because of a body-swapping event that had the two switch. While they are attacking Daredevil, Spider-Man and Thor get involved in helping defend Daredevil and a massive 3 on 3 fight commences. During that fight, the Thing gets knocked into a cannon that Richards calls the Demolo-Gun and sets it off. He instructs the Thing to destroy it before it goes off because it would have leveled all of New York right then and there. We never actually got to see the Demolo-Gun in action, but apparently, it can pack quite the punch.
6 Parker Particles
The Parker Particle is a hyper-kinetic form of energy that Reed Richards originally discovers, but keeps it secret because of the danger he fears it holds. They are tied to the expansion of the universe, so as the universe continues to expand, they get stronger and more dangerous. Unfortunately, down the line, Peter Parker discovers them and sees them as a way to have "Clean, affordable, near-limitless power." After trying to display the power of the Parker Particles, a high school kid named Andy Maguire gets shot with a ray of the Peter Particles that gives him immense powers and thus the superhero Alpha is born.
5 Negative Zone Prison
The Negative Zone Prison is in an alternate dimension and is designed to hold the superheroes that refused to register during the events of Civil War. It was designed by Reed Richards, Tony Stark, and Hank Pym. Named Project 42 by Stark, the inmates had very sarcastic names for it including "Wonderland" and "Fantasy Island."
Until Captain America breaks in and leads a prison break for all the superhero inmates, there was no real hope of escape for everyone within. Three of the greatest minds in the world built the prison, it was heavily guarded, and passwords for every cell were automatically changed every ten minutes.
4 Thor Clone
Another Richards, Stark, and Pym creation that did not look too good on any of the high profile mind's resumes. During the events of Civil War, Thor went missing, many presumed he was dead. To help push their registration agenda, the three used a piece of Thor's hair that Tony kept since the original Avengers meeting to clone a new Thor and put him into a cybernetic suit.
The three used the Thor clone to battle any heroes who were against registering and often he would take them down easily. Things got out of hand though when the clone killed Goliath and set out to kill the rest of the anti-registration heroes. Richards shut down the clone to work on his brain to prevent any more killing from happening, but the damage had already been done. Hercules and Storm would later destroy the clone by pounding him in the face with his hammer.
3 Afterlife Transporter
Leave it to Reed Richards to find a way to teleport to the afterlife. Following the death of Ben Grimm, AKA the Thing, Richards is in a bad state. He is blamed for Ben's death and the other members of the Fantastic 4 no longer trust him. In an attempt to bring Ben back to life, Richards steals his body from the army, hooks it up to a machine, and builds another machine that brings them into heaven where they have to undergo many trials and tribulations before having a conversation with Jack Kirby, who is God.
This machine is not powerful in the sense that it directly puts people in danger, but it literally is used to bring someone back from the dead. I would say that is powerful enough.
2 Atomic Space Displacer
In Fantastic Four #32, Sue and Johnny's father, Franklin Storm, has been kidnapped by the Super Skrull who then transformed himself into Franklin and took the guise of the Invincible Man to try and divide the Fantastic 4. It does not take Reed Richards too long to realize what is happening so he then begins working on the Atomic Space Displacer.
After defeating the Super Skrull, Richards gets in contact with the Skrull homeworld to negotiate a prisoner exchange. If the Skrulls did anything out of line during transporting Franklin back home, Reed threatened to use the Atomic Space Displacer that appears to be a nuclear weapon capable of destroying an entire planet. Not too bad for only making it in three hours.
1 Anti-Matter Injection System
During the events of the Incursion, Reed Richards and the rest of the Illuminati are trying to find the best way to prevent other universe's Earth's from colliding with their own. After Black Panther witnesses Black Swan using some technology to destroy another Earth, he and Richards reverse-engineered the technology and created their own version of the Antimatter System which they intended to use to destroy other Earth’s before they smashed into theirs.
Richards and T'Challa did not take into account the fact that they would be killing billions of human beings, though. When it came time to use the Anti-Matter Injection System and save their Earth, they were unable to do so. Namor, however, had no qualms with sacrificing another Earth so his may live on.