Create relationships between the characters. Maybe there are two crew members who have a love - hate relationship. As the story progresses, this relationship can evolve. They could start off arguing but then come to rely on each other during a crisis in the Titan submarine, which would show growth and development in both characters.
A survival - themed plot could be interesting. For example, the Titan submarine could get stranded in an unexplored part of the ocean. The crew then has to deal with limited resources, strange underwater phenomena, and their own internal conflicts as they try to find a way to be rescued.
Well, it depends on the specific story. Some 'phantom submarine' tales might be based on real submarines that were involved in covert operations. For example, during the Cold War, both sides had submarines doing secretive patrols and surveillance. If one side detected an enemy sub briefly and then lost track of it, it could be called a 'phantom submarine'. So in the context of a true story, it might be a real military sub.
A really cool submarine book is 'Voyage to the Bottom of the Sea' by Irwin Allen. It has a lot of exciting adventures and scientific exploration as the crew of the submarine Seaview faces various threats and mysteries. It combines action, science, and adventure very well.
It could be a lost or abandoned submarine. Maybe it was part of a military experiment that went wrong, and it's now drifting around, appearing and disappearing like a phantom.
The Ultimate Titan and the Hell Titan were the two BOSS characters in the Giant City Ruins Challenge Mode in Cross Fire. The Ultimate Titan was the BOSS of the 16th checkpoint of the Giant City Ruins. It had many skills, including Charge, Cannon, Energy Ball, Shield, Hell Cannon, and Thunder Pool. The Ultimate Titan's Charge skill had three enhancements. It could move three times and cause a small-scale explosion after colliding with an enemy. The energy ball was a slow-flying energy ball launched by the Ultimate Titan. It attacked the player with the furthest distance. The shield was generated after a certain amount of HP was lost, and the HP bar turned blue. After the shield was broken, the original red HP bar would be restored. The Hell Titan was a skill of the Ultimate Titan. It was a camouflage created by the Ultimate Titan, not a real body. The Ultimate Titan and the Hell Titan were both important characters in the Giant City Ruins Challenge Mode. Players needed to be careful when dealing with their skills and attacks.
In the game Titanfall 2, players could exit the cockpit of the Titan mech by pressing the square button on the controller or the "E" button on the PC. This way, he could leave the Titan mech and continue to operate or fight.
The Titanfall had three types of Titan Mech bodies: Ranger, Sky Map, and Giant Demon, which corresponded to Light, Medium, and Heavy Titans respectively. In addition, there was also a Titan Destroyer, which was a derivative of the Giant Demon level. These Titan Mechs had different characteristics and abilities in the game.