Nautilion (Oniverse series of solo games). A look at the artwork, expansions, gameplay and subs.

About Nautilion, from BoardGameGeek:

Description from the designer: Nautilion is a dice game in the Oniverse series! Take the helm of a Nautilion submarine and recruit a heroic crew to vanquish the treacherous Darkhouse that lurks in the oceanic depths. You must get to the Abyss, lair of the Darkhouse, before the Phantom Submarine (his henchman) reaches your homeland, the Happy Isles - but to defeat the Darkhouse, not only must you be faster than the Phantom Submarine, you must also assemble the submarine's crew along the way. Each turn, you roll three dice and give one to each of these figures: the Nautilion, the Phantom Submarine, and the Darkhouse. The dice of the Nautilion and the Phantom Submarine move those figures along a path formed by Crew tokens: the Nautilion from the Happy Isles towards the Abyss; the Phantom Submarine in the opposite direction. The crew token on which your Nautilion ends its move joins your submarine, the one the Phantom Submarine reaches is lost! Only four copies exist of each of the nine different tokens, so you have to decide carefully which die you need and which you can leave to your enemies. (The Darkhouse doesn't move, but inflicts damage to you each time he gets a die with a high value.) To win, you need to reach the Abyss with a full crew of nine different tokens. Five expansions are included with the game, adding new crew members, powers, treacheries and challenges.