Im mostly using felt tip tech pens or a Copic black marker to do the line work and fill in blacks. They aren't as super black as they appear here. I just bump up the levels and contrast to knock out the gray of my underdrawing and make the blacks nice and dark. When I ink pages and covers I use Speedball Super Black india ink for my large black areas. It does come out this black on the original, but you have to be comfortable with a brush to ink that way.
first of all let me congratulate you on the amazing piece, snake eyes looks great, his pose is unique and karate kid is looking awesome, what i really like is the action itself, there's tension, and a challenge feeling, i bow in admiration to your skills in doing this piece