atariland2600 has updated his game GoSub2. It’s now at build 71a.

Release notes:

Well, after three hours of trial and error, I finally figured out how to make the sub move through the octopus and shark slowly. The shark sprite is a temporary one until I find a better one. As for one enemy being confined to the walls like the sub, how would the intro work? The intro being once the level starts (or it’s shot), it enters from the side.