Who: Hank McCoy When: Around 1990, winter Where: NYC What:From Human to truly Beast
Beast was twenty-one, and feeling his more independent, and almost bitter side of being a mutant, and trying to do good for humans. So, because of this he went off like a lot of the X-men did off and on and for short periods in their X-men careers. He went off to be a genetic scientist at the research facility called Brand Corporation. He was working for months almost a year on a "hormonal extract" allowing anyone to become a mutant for a short period of time. He almost had it where he though he might be able to test it on someone. However, he didn't know who at the time, it wouldn't work as well on animals, and it was sort of tricky figuring out how much would work and so on and so forth.
One night he was working late in the lab and he heard noises, which he went to investigate. While he was doing such he found that it was two young mutants that had somehow heard about his research. They wanted to try to duplicate his research, mass produce it and then set it out for all humans to see what it felt like to be a mutant for a while. Hank didn't want this to happen, so he went after them, deciding that he would take some of his work. He chased them around, finding that the potion had given him gray fur all over his body and acquired sharp ears, elongated canine teeth, claws. Along with this physical transformation he also gained the ability to run on walls and ceilings like a spider, enhanced senses.
Hank now knew how it felt to be Wolverine. He could smell, and hear extraordinarily better then he had before. Probably not as good as either Wolverine, or Sabertooth as they were real feral mutants, and Beast was manufactured as such by taking the potion, but still it gave him some edge on the intruder. However, he still liked it, or at least for the time being. It made it easier to track the ruffian, thief. After an hour running around he caught him, restrained him, and left him outside for the cops to find after he had called them. He then hurriedly went back to his lab to reverse the effects.
However, when he got back to his lab, and took the antidote he found he had waited to long to reverse the effects. He also noticed that the fur that was original grey had turned blue, and he was slowly having more feral feelings and tendencies. Later on down the road he would also find out that he had an accelerated healing factor to a certain extent, not as strong as Wolverine's or Sabertooth's by any degree, but it did help him to heal from some terrible injuries faster then most would.
Eventually he went back to the X-men shortly after the mishap as it made him now look like an extreme mutant and he noticed it made the human's nervous to be around him. Plus he felt that his knew abilities could help in the fight against the Sentinels. So, back to the X-men he went, and has been with them ever since.