It's kind of a simple answer- Sure, they look the same. But if you wanted a deeper connection, every re-release of Cave Story made by Nicalis has Balrog call Jenka his aunt, in some format of the term. That doesn't exactly seem like a taunt, and if there is truth to that statement, that would raise a few points. Balrog and Jenka have a connection as family. Balrog and Misery are cousins. Recall that Jenka and Ballos are siblings. Ballos is probably Balrog's father. But then that raises a small contradiction: In every version of Cave Story, Ballos mentions that both his wife and children were killed by his magical tyranny. So if it were true that Balrog were the nephew of Jenka, he would have had to survive that. For the sake of entertaining this idea, let's say he did that somehow. That still leaves dead children and a dead wife. Which would raise even more points. Puu Black looks like Balrog. The only way this thing described in-game is as a ghost. It inhabits the Island. Sure, it seems like a really far-fetched coincidence, but Balrog and Puu Black might be siblings.