I used a Pentel brushpen for that. But a lately I've been using a Windsor & Newton watercolor sable. You can get a bit more range out of them. They are kinda pricey on Jamaican standards but well worth it if you are serious about making the next step with your work.
awesome dude. i'm really liking your brush work. it's cool to see you develop and switch your styles up from time to time. i wish i could do that. oh and the one in blue in the top left and the one with his arms stretched out in front of him are the coolest. keep it up man, great stuff!