In response to the stage itself though, allow me to point out a couple flaws in your proposed design.
First of all, assuming the fish eating the player equates to death, non-blastbox deaths outside of stamina matches are usually not well executed. I use SSB4's Great Cave Escape as an example, as well as the fight with Master Fortress. These detatched death-boxes are often comboed/knocked into with relative ease and not only make fights unfair for certain fighters, but make them unbelievably fast. It's the situation you see with many walk-off stages. Fighters could grab-throw, grab-release, or do really anything with little executional skill at low percentages to kill others.
Speaking of walk-offs, platforms that glide off-screen are pretty shaky as well. All it takes is a grab-release, or even a simple grab-and-hold to take somebody off stage. Once again pointing to SSB4 stages, Kalos League and Town & City are good examples of why this is unbalanced and ultimately unoptimal. Stages with transformation and travel are usually a bit more balanced because it's much harder for a character to survive their own grab-release.
Also, I don't find much solace in knowing that this would be Crusade's first water-based stage (if I'm not mistaken). If we're going to have a dominantly water-based stage, I definitely don't want it to from this extremely forgettable game.