This game is cool! I know you may not be proud of your art, but I find them to be quite fun to look at. I actually clicked on this game because of the thumbnail :D. I see a good sense of design, and the game holistically looks good for game jams' standard.
Fusion is a very good idea. It is fun to see the deck getting stronger as you fuse cards. One improvement you can make is to present the game mechanics better visually. I didn't notice the stats at the corner at first. I think if how the game works is explained better, I wouldn't be stuck for as long.
Sailing around was fun, and I like the photo of a dude on one of the ships. It seems like you had fun making this game, and that's all that matter!
Overall, a very fun card game. Great job!