Doctor Palance's expertise in genetics was sought out by Charles Xavier regarding Rogue's condition when she first joined the X-Men. Instead of helping her, he used her DNA spliced with a virus to give himself her power absorption abilities. Drunk on power, he realized that he could attain immortality by absorbing other people's lives, then creating the Strain 88 Virus to do so. At first, he wasn't completely sure Strain 88 would work, so he used Rogue as a test subject.
Soon the X-Men located him and fought him, in which he revealed he had over 300 powers absorbed. Defeated, all hope was thought lost until Cable threw Sabretooth at Pan, knowing he would absorb Creed's powers. But Pan was unaware of Sabretooth's healing factor, and thus the virus was expunged from his system and rendered him completely powerless when he absorbed them. When Lady Mastermind realized he was the one responsible for her being comatose for over a year, she then left his mind stuck in an illusion.
However, he was later asked for help by Beast on creating a cure for after M-Day. He declined though, saying the X-Men ruined his life work so why should he help them.
Power Absorption: Pandemic was able to absorb the powers of Mutants via physical touch. Pandemic himself is not a Mutant, and was only capable of absorbing Mutant powers due combing the DNA of the X-ManRogue spliced with with a virus to give himself her power absorption abilities.
From the over 300 Mutant abilities Pandemic was known to possess were:
17 forms of Invulnerability: Obtained from 17 unknown Mutants.