Submarines are available to players in free companies through their shared workshops in Final Fantasy XIV. Free company members can send their submarines out on voyages or ventures to find special rewards. Among those rewards is the Syldrion-class Insubmersible minion, modeled after the same submarine craft. There’s a bit of luck involved with getting this minion on your own.
Obtain through Submarine Ventures
One option is to send your free company submarine on ventures and hope it returns with the Syldrion-class Insubmersible minion. It may take some luck and patience to get the minion this way. Of course, if your free company doesn’t have a submarine (or if you’re not in a free company at all), then you’re completely out of luck. This is the only way to obtain the minion without paying. If this option isn’t open to you, then you’ll just have to shell out the gil needed to buy the minion instead.
Buy the minion on the market board
This is your other option, in case the submarine ventures aren’t available to you. It’s possible that the prices will continue dropping over time. So, you may want to wait a bit and save up some gil while you can. Or, you can just shop around on the other market boards on your data center, using the World Visit system. But due to the amount of luck involved with obtaining the Syldrion-class Insubmersible minion, there’s no real way to tell where the market will go. However you obtain this, use the item itself, and the Syldrion-class Insubmersible minion will be yours.