The past of Baco Shot is unknown, but what it known is that he was ne of the most dangerous criminals around. So dangerous in fact that when the government captured him he was sentenced to level 6 of Impel Down. The most dangerous level, were his crimes and all memory of him was erased from history.
Upon the arrival of the Blackbeard pirates at impel down during Luffy's attempted rescue of Portgas D Ace. Marshal D Teach made his way to level 6, were he made each cell fight a battle to the death, promising each victor that he would take them on his crew. Basco Shot was one of those victrs and became a member of the Blackbeard Pirates.
Arrival At Marineford
During the war between the marines and Whitebeard pirates. Basco Shot along with his new crew and other level 6 escapees arrived. Much to the shock of the marines who began identifying each one. Basco Shot asking if it would be ok to kill them. He then assault Edward Newgate with the rest of his crew. After Whitebeards death he helps his captain cover up his body, so that he can gain Whitebeards Power. As Teach uses his newfound power, Basco and the others are attacked by Sengoku. Later during the arrival of Shanks he leaves.