Splashdown: The only real way to counter this one is to just outright shoot it down there's a quick delay once the user reaches the peak of the rise depending on your weapons speed you may be able to hit a couple shots during that phase and secure the kill if you see it coming but don't react fast enough try your best to get out of the range of it even if you don't avoid it entirely you may still be able to escape the lethal range of the shockwave which from there you can run away and recollect yourself or although I strongly advise against this try to finish them off if they are weak already. I would recommend stuff with range or fast fire rates depending on if you prefer to avoid or kill but I recommend something with at least 3 blocks of range.
Baller: Not gonna sugar coat it the only way to really stop it is to destroy it entirely. I find the best weapons to do this are longer ranged splatlings(heavy, hydra, ballpoint etc.) as it allows you to hit them from a distance while also hitting a lot of shots in a short time
Bomb Launcher/rush: If your opponent panics in the middle of it they may forget they can use their main weapon in this case rush in and smartly avoid their bombs and just take them out. Anything should be ok for this situation
Bubble blower/Tenta missiles/Ink armor/Ink storm: If they activate it too close to you take them out also you can just avoid tenta missiles by literally walking away from the markers maybe having to swim just before the crash down depending on how much run speed you have. Bubbles you can kill by shooting. Be careful of ink armor though because they can shoot during its activation.
Inkjet: Most of the time it's better to just avoid if possible but if you the opportunity to kill them just zigzag to avoid their shots and shoot them down when you get them in your range.
Stingray: Imagine stingray as a tap shooter but actually good to beat it just get them in your range and circle them and track them as you circle them to secure the kill. if they are somewhere where you can't get to them you may be able to throw bombs to try and kill them as well also if you could use a special weapon but I personally would use a special to try and hit one person unless it's absolutely urgent. again any weapon can work and specials if god forbid you're ever in that desperate a situation I'd recommend ink storm, a perpendicular sting ray tenta missiles or bomb rush.
that's it for this guide. If I missed any let me know.