CAPTURE THE ZAPFISH
Each team has a Zapfish on their side of the map, which must be taken by the opposing team to a generator on their side to score a point. After a point is scored, the Zapfish lightnings back to its starting position and the process begins anew (for the team that just scored anyway; their own Zapfish does not auto-return when they score, so it's possible to steal the other team's Zapfish while they have yours and not worry about losing it when they score). There would be a maximum score, at which that team wins by knockout, I want to say 3-5, but I'm not sure on the exact amount.
The Zapfish would have to be carried by an Inkling, which is done by touching the Zapfish. The Inkling holding the enemy team's Zapfish is slowed down and unable to swim or attack while holding the Zapfish, but they can throw it like a Bomb-type sub-weapon with R (which, yes, is affected by Bomb Range Up); you can score goals by throwing the Zapfish into the goal as well as walking it in there. You cannot pick up your own team's Zapfish, but if it's left alone long enough the Zapfish will begin flopping toward its starting point; if it falls off the stage or does not move forward for 2 seconds, it lightnings back to its starting point. Additionally, the player who takes the Zapfish from the enemy team's Zapfish starting point gets a 2-second Bubbler (not affected by Special Duration Up) to ensure they get at least some distance away from the enemy's starting point with the Zapfish; also, if the Zapfish has started flopping away to its starting point, then picking it up grants a 2-second Bubbler as well.
Overtime can only happen if the losing team is one point away from tying the match and has the Zapfish or if there is a tie, but the less-recent-scoring team has the Zapfish; if both teams are tied and that isn't the case, the team that scored last wins, and if one team has a higher score when time runs out, they win. During Overtime, the losing team must get the Zapfish into the winning team's goal, which gives them the win because during Overtime, the Zapfish grants 2 points. The winning team can prevent this in one of two ways. Firstly, they can keep the losing team away from their Zapfish long enough that it flops back to its starting point. Secondly, they can score a goal with their own Zapfish, and since the losing team is no longer within 1 point of winning as a result of this (both Zapfishes become 2-pointers in Overtime), the winning team automatically wins (though not necessarily by knockout, unless they reach the knockout score by doing this).
Certain stages would have to be altered for this mode, though mostly just keeping the Ranked versions would probably be sufficient. I'll go over the stages here (only the stages we currently have, so no Flounder Heights/bridge stage, and also only text, since I can't do images at the moment: I'll do the best I can with explanations, but sorry if it's kinda vague anyway):
Arowana Mall: The Ranked version of this map might be alright: each team's Zapfish would start in the alcove to the right (you can go into the center, then take the ramp on the right to reach it, hope that helps), and each team's goal would be in the center of that lower area in front of the spawn point (just go straight forward and it's right there).
Blackbelly Skatepark: Each team's Zapfish would start just behind the halfpipe area off to the left of the spawn point (so you'd have to go through the halfpipe area, or around from the center entrance if you went in a straight line betweenspawn points), while the goals would be in the area just above the halfpipe area (go through the halfpipe area from the spawn point, then ink up, then turn left and it would be there).
Saltspray Rig: This one is one of the tricky maps for me, because both teams start on the same side. I think the Ranked version of this stage (I think there are some changes, though I don't know for certain) should suffice. The Zapfishes would start on opposite sides of the furthermost platform, and the goals would be on the ends of the spawn-point platforms' long protrusion (to the left on the left team side, to the right on the right team side). This would require throwing the Zapfish to score, but I'm not sure of a better option on Saltspray.
Urchin Underpass Classic: Mostly here for the sake of completeness. The Tower Control version of this stage would probably be best. The Zapfishes would start in the lower area in front of each team's spawn point (it has a grate and a ramp on its left, if that helps locate it), and the goals would be just in front of the downramps in front of the spawn points.
Urchin Underpass (new): The Zapfishes would start in the same area as they did for Underpass Classic, but the goals would be moved to the side paths (leftmost from the spawn points) in that alcove across from the grate-wall.
Walleye Warehouse: Another toughish one, since it's smallish. The Zapfishes start in the alcove under the grate flooring (go left from the spawn point and take that path to the grate, then drop down, and you're there), and the goals would be just in front of the ramp in front of each team's spawn points. Not entirely sure it's good, but I think it might be okay.
Port Mackerel: The Tower Control version of the map would be used, but with the forklift-things (I think those are forklifts) from Turf Wars added back in. The Zapfishes would start at the end of each team's right-side corridor (where the inkable boxes are in Tower Control, ink up it, then jump up and you're pretty much there) and the goals would be just down the ramp from each team's spawn point (you would see it just in front of the box when you respawn, if that helps).
Kelp Dome: The Splat Zones verion of this map would be used solely to make it easier to get into the center. The Zapfishes would start at the end of each team's right-side corridor from the spawn points (just behind the ramp up to the grate-catwalks, if that helps) and the goals would be in that squareish area to he right of the spawn points. The idea here is that it's significantly more difficult to reach the Zapfish than on most maps, but also easier to score when you get it; dunno if that's how it would end up working out, but maybe it would.
Bluefin Depot: A modified Tower Control map would be used, with the bridges off the center areas being longer so Inklings can jump between them. The Zapfishes would start in the area just before the center (in the middle of the ramp connecting both sides, if that helps), and the goals would be the top of the staircase in front of the spawn points.
Moray Towers: The Splat Zones version of this map would be used, though admittedly that's solely because I prefer it to the normal version. The Zapfishes would start on the platform overlooking the first platform up the ramp from the center on each side (you can ink up to it from the Splat Zone, if that helps) and the goals would be placed at the halfpipe roughly halfway up the ramps (not on the halfpipe, just in front of it).
Camp Triggerfish: The floodgate further from each spawn point would be down for the entire match, while the closest one would remain up for the entire match. The Zapfishes would start in the circle area off to the right of each spawn point (right on the little circle-table-thing in there) and the goals would be on each team's floodgate-platform (the one you reach by inking the floodgate closest to the spawn and swiming up it, it'd be right where the glass is).