Overall tip.
1. Take time at the start and between phases to ink the ground.
2. Strafe, strafe for you life. And learn solid aiming.
3. Get used to the general distance they will dodge roll.
4. Bunny hop between ink puddles is kind of needed.
5. If your armor breaks, unless you're certain about confirming a splat, better run. A single shot or the splash from an Autobomb will speak doom.
6. Be aware when Agent 3 has their special ready, this is a good indicator of when your should either rush or flee.
Phase 1.
1. After the splashdown, swim up diagonally then try to deal as much damage fast. If you see that you're getting hit, not even broken armor, best to retreat for a little healing and try for another attack. Best case scenario you can splat them before or right as they Inkjet.
2. If they do Inkjet, the two obstacles on the map are your friend. Dance around them while Agent 3 wastes their Inkjet.
3. Note that Agent 3 will always fire exactly 6 shots before returning to their launching point, know this and be prepared to camp the point when Agent 3 lands.
4. Get used to the general distance they will dodge roll, especially after the Inkjet, that is prime opportunity to get a lot of damage in.
Phase 2.
1. This one is actually quite simple, Agent 3 will always get a Bubble almost immediately, attack them from the side. You can get a lot of damage in with this. Agent 3 is effectively helpless while tossing out bubbles.
2. However, once the third bubble is thrown, it is advised not to be close to it, Agent 3 will throw an Autobomb and it will explode immediately. Either flee or be on the other side of Agent 3.
Phase 3.
1. Try to rush them down when they're using Autobomb Launcher, BUT be cautious that Agent 3 can still use their main weapon.
2. This phase is probably the least consistent, just try to rush and end it fast, hope that Agent 3 struggles to decided to use their main or special.
3. I do find that there is a bit of a Goldilocks zone, where you can hit Agent 3, but they won't try to use their main.
Phase 4.
1. Make sure you have ample ink coverage to recharge your ink.
2. Throw a Splat Bomb at Agent 3 while their platform is about to reach its first destination, just as they use the Tenta Missiles.
3. Recharge ink as the missiles come down and you should be able to throw a second one, effectively splatting Agent 3. Key is just to get 2 Splat Bombs fast.
Phase 5.
1. Take advantage of the blessed obstacles on the map. Splashdowns cannot deal damage if you're on the other side of a wall. They'll still ink the ground, but you will not receive any damage.
2. After Agent 3 does their 3 Splashdowns, rush them, apply pressure.
3. Whatever you do, stay close to one of the obstacles. Agent 3 can do a panic Splashdown when their health is low.
4. Be very aware if Agent 3 has their special ready, especially on this phase. The panic Splashdown mentioned above requires Agent 3 to auto recover their special first before using it. If you see glowing hair, hug a wall and be prepared to take cover.
5. Finish it!