Answer by Urmi Goswami:
No character is worst in Mahabharata. Remember the law, "For every action, there is an equal and opposite reaction", same was the case in Mahabharata. All characters were grey and all characters were neither too good nor too bad. Some or the other character had a tragic back story or was humiliated or was cursed and many other things. The most important thing is that the epic does not tell about the worst or the best character, it teaches us about mankind, about an era, about Dharma, Adharma, satya, asatya, kalesh(to cause agitation) and many more.I read a few answers before writing mine, some say Shakuni ,Duryodhana, Ashwattama,etc. are worst. I agree they were evil but their deeds and destination are the ones which make us realise the difference in good and bad. In the Mahabharata era, the principles of religion had declined to one-half so it's obvious that there existed evil. A yuga learns from the preceding one. So,today we are in the kaliyuga but we learned from Dwapara yuga and the preceding yugas.So, no worst or best characters but a character worth learning and understanding!!