How did hank mccoy mutate into beast?

Answer 1

When Hank left the X-men, he went to research genetics at Brand Corporation. He worked with Dr. Carl Maddicks. He then isolated the extract that created mutations, turning into a serum that would temporarily activate latent mutations for short periods (though it had an antidote). He overheard Carl Maddicks wanting to steal his research, so he took the serum himself, trying to disguise himself, and instead underwent "horrible" radical changes. He lost track of the time, and found the time had passed for him to take the antidote and was now stuck in this form. Angry at this turn of events, he lashed out, almost killing Dr. Maddicks, though he was stopped in time.