Age of Apocalypse
In the alternate dimension he came from, Hank McCoy was a mad scientist working for Mister Sinister in his breeding pens, intent on breeding more powerful mutants according to Apocalypse's "survival of the fittest" dogma. However, while Sinister was methodical and rational in his experiments, McCoy (as ruthless as his mentor) sadistically delighted in causing pain to his lab subjects and in the cruelty of his experiments, which is why he was nicknamed the Beast both by prisoners and Sinister's Elite Mutant Force. McCoy also experimented on himself in order to further his mutation, and gained his ape-like bestial appearance. Any mutant that he deemed unworthy was turned into a component of a genetic stew that was used to create Apocalypse's army of Infinites. Besides being one of the creators of the Infinites, the Dark Beast also experimented on Blink, on Jamie Madrox (thus being one of the creators of The Madri), merged all of the Power siblings into one hideous creature, made Nemesis into Holocaust following his defeat at the hands of Magneto, and was also responsible for the creation of Holocaust's lead hunter Wolverine (not to be confused with the X-Men's Wolverine who was known only as Weapon X in that reality).
With the end of the Age of Apocalypse, the Dark Beast was able to escape into Earth-616 through the M'Kraan Crystal. He was believed to have died due to Quicksilver's interference in his set trajectory. However, the only damage was that he landed twenty years in the past in the Morlock Tunnels. Upon his arrival he was met by a young Emma Frost, who helped him to regain some of his scattered memories. The Dark Beast was responsible for the creation of the Morlocks. The characteristics of the experimentation were later recognized by the 616 Mister Sinister as an unauthorized use of his own theories, leading him to order the elimination of the Morlocks. The Dark Beast later kidnapped the real Beast and kept him a prisoner behind a brick wall. He infiltrated the X-Men in his place by altering his appearance to match the real McCoy's fur color. He helped keep up the ruse by slaying many of Hank's childhood friends and teachers, although he found himself unable to kill Hank's parents. Angered at this emotional weakness, he decapitated a pedestrian as he left town. The Dark Beast was able to keep up his ruse until the Onslaught Saga, during which the Dark Beast joined Onslaught. Onslaught had, in fact, known from the beginning of Dark Beast's ruse and mentally shielded him from other telepaths at the mansion. He also had a few run-ins with Generation X and Gene Nation. There he was the leader of the newly revamped Gene Nation, although through the robotic body of Wynter, attempting to capture Generation X in order to experiment on them. The previous meeting between him and Emma Frost was also revealed. He also led an incarnation of the Brotherhood of Mutants. Right before House of M, the Dark Beast was in Genosha where he joined Xavier's team after being offered parole. It was confirmed in The 198 Files one-shot that he stayed powered after M-Day.
Allied with Hank
Dark Beast returns and finally confronts his counterpart in the Endangered Species storyline where he ambushes him in Neverland, the extermination camp ran by Weapon X, to offer his services regarding finding a cure for M-Day. The two form an uneasy alliance to tackle the impending mutant extinction but part ways due to their drastically different moral approaches to science. During a trip to the Guthrie household aimed at requesting samples of DNA from the mother and father of several mutant, and non-mutant, children - the Dark Beast (without warning Henry) poisons one of the un-mutated Guthrie boys in a quick scientific experiment. He then carries the dying boy's body back to the house, suggesting that they should try one of the girls next. Shocked and enraged with his actions, Hank attacks the Dark Beast who, disgusted with Henry's inability to do all that is necessary to save their mutant species, beats him almost unconscious. The fight is interrupted by Mrs. Guthrie, who fires a round from a double-barrled shotgun into Dark Beast's left shoulder. After scolding Mrs. Guthrie for thinking a round of birdshot would put him down, the Dark Beast is knocked unconscious by Henry. The child is saved by Hank.
Dark Beast later appears as a member of the Dark X-Men, a team of X-Men put together by Norman Osborn. He serves as the team's scientist. He constructs a device known as the "Omega Machine" to experiment on mutants in Alcatraz for HAMMER and starts testing on Beast, causing him great pain and torment as it begins slowly eating him away. Osborn is not impressed with the test results of the Omega Machine and wants Dark Beast to make sure the machine works in removing powers from mutants, not killing them. Dark Beast continues to experiment with his Omega Machine, using Beast as his key test subject. Each use of the devise causes Beast to look more decrepit and weak. Deciding to use a new subject to test the device on, Dark Beast goes to collect the newly captured Mindee of the Stepford Cuckoos. When he reaches the holding cell however, he discovers that Mindee's capture was done to allow X-Force to follow. Dark Beast is then attacked and stabbed multiple times by both Wolverine and Warpath.
Powers and Abilities
McCoy possesses a number of superhuman physical attributes similar to those of his mainstream counterpart. However, McCoy continuously subjects himself to genetic alteration experiments, so the full scale of his powers often remain in a state of flux.
Superhuman Strength: McCoy is superhumanly strong and his strength has increased considerably due to his own self-experimentation. Originally, he possessed the same level of physical strength his mainstream counterpart originally possessed and could lift approximately 1 ton. He currently possesses superhuman strength equal to that of his counterpart prior to undergoing the mutation gave him his current feline form. At his peak, McCoy can currently lift about 10 tons.
Superhuman Stamina: McCoy's musculature produces less fatigue toxins during physical activity than the musculature of an ordinary human. He can exert himself physically at peak capacity for several hours before fatigue begins to impair him.
Superhuman Agility: McCoy's agility, balance, and bodily coordination are enhanced to levels that are beyond the natural physical limits of even the finest human athlete.
Superhuman Reflexes: McCoy's reaction time is enhanced to a level that is beyond the natural limits of even the finest human athlete.
Superhuman Durability: The tissues of McCoy's body are somewhat harder and more resistant to injury than those of an ordinary human. While not invulnerable, he can withstand impact forces and blunt force trauma that would severely injure or kill an ordinary human with mild to moderate discomfort.
Accelerated Healing Factor: If injured, McCoy is capable of healing mild injuries faster and more efficiently than an ordinary human. His body can heal roughly twice as fast as the body of an ordinary human. His self-experiments have also resulted in extending his longevity by slowing his natural aging process to an unknown degree.
Pheromone Manipulation: McCoy possesses the ability to secrete pheromones that causes members of the opposite sex to become attracted to him. The full limits of this ability isn't known but it is one that his mainstream counterpart possessed at one time.
Claws & Fangs: McCoy possesses elongated canines and razor sharp, retractable, claws at the tips of his fingers and toes. He is able to use these claws to cut most conventional materials including flesh, bone, wood, and stone.
McCoy is a skilled geneticist capable of numerous experimental techniques of genetic alteration, mutation, and combination.
Dark Beast possesses a counterpart in the Mutant X Universe, who also allied with the Mutant X Hank McCoy (The Brute) to undo the effects of that reality's M-Day.