So, I stumbled across this video on YouTube today. I know it is an old video, but thought I might share it as it is awesome.
Do you agree with the video? What are your top 3 choices for deadly pokemons?? 
3 Pokemon Who Could Kill You - Vsauce3
Wait! There are some more?
Most of the guys videos are on the potential to kill you. Every Pokemon has that potential, the thing that going to make them deadly IMO is what’s their motivation.
Gengar is number 1.
Gengar’s Fire Red entry where it says: It is said to emerge from darkness to steal the lives of those who become lost in mountains.
Literally in the entry it tells you this thing kills people who are lost. That’s enough for me to put it at number 1, as there’s no challenging it, no confronting it, just if you happen to be near this thing in the wrong situation it’ll flat out murder you.
Mewtwo is number 2.
Mewtwo’s Fire Red entry states: A POKéMON whose genetic code was repeatedly recombined for research. It turned vicious as a result.
Take the most powerful pokemon around and make sure it hates people. Easy motivation for Mewtwo to kill anyone it sees, the only reason it’s not number 1 is there’s only one of them.
Beedrill is number 3.
Beedrill’s Ruby/Sapphire entry says: BEEDRILL is extremely territorial. No one should ever approach its nest - this is for their own safety. If angered, they will attack in a furious swarm.
Not as dangerous as Gengar or Mewtwo who will probably come at you for no reason, Beedrill will still kill you if you just happen to get to close to a territory.
Just missed the cut, Raichu - who when overly charged gets aggressive, however he often discharges from his tail so it doesn’t happen much.
Electrode - who explodes at random.
I only looked into first gen pokemon, and used poke entries that were easy to uncover through serebii.net
I would have to say Mewtwo is the most threatening. He was the nemesis in the first movie. He turned Ash into stone, and left him there to die. He can speak to humans, and can talk shit like Vegeta.
For me. It’s easy. Smoochum. Kiss of Death. I reckon I could hold my own against any other pokemon provided I had a tank 
to quote Stan Lee “nuff said”
Easy question on the deadliest. Hoopa in unbound form is able to manipulate reality.
Nothing can beat him. 
You know what… I disagree because when I got some PSA 9s and asked hoops to turn dem into tens he didn’t answer me back. I is angry with dem 9s and I want an explanation.
I think metapod would have a pretty hard time killing you. Maybe he’d get so hard (teehee) and sharp that you tripped and impaled yourself?