The first thing that comes to mind when Port Mackerel is mentioned is its hallways. This map consists almost entirely of narrow corridors criss-crossing each other. Either keep your distance by zoning foes out with ranged weapons, or use sharp corners to get the jump on enemies.
Layout
The area around spawn is moderately spacious and slightly raised, with four paths leading out of it. The two middle paths go straight forward, with two more hallways connecting them. Two flank routes are also available to the left and right above ground level. They sometimes branch out to the central paths, but ultimately ends at the large clearing of each team. These clearings are the only open areas on the map. They are rectangular and wide, with three bumps placed at the middle.
The center of the stage consists of three paths through a grid of containers, along with three horizontal paths connecting each. There are little nooks along the paths for cover. It is possible to get on to most of the containers on this stage, but they can't be inked.
Mode strategies
Turf War
Turf War has two barriers separating the bumps at either team's clearings. It also has a pair of vehicles moving through two of the horizontal paths at the center, which can push players and block shots. The vehicles can be inked, letting players get on the vehicles or reach the top of the containers.
Port Mackerel presents a convenient layout for the starting push. There are four paths leading out from spawn, one for each player to take and ink, but multiple players can go down the same path if speed is a concern. Rollers, brushes, chargers and Seekers are great for quickly inking the straight pathways. The area around the spawn is a good place to place Sprinklers since it is a wide open area that isn't worth the time to have a player present inking it. Each team's court outside the middle grid is a safe place to build up Specials, but you'll want to quickly focus your efforts on the central corridors.
Try to make sure that the three corridors leading into the center of the map is always inked. They are the only paths that connect the two team's bases together and a lot of the battle will involve crossing the grid to the other side. Long-range weapons can be an effective deterrent against enemy approaches, while Seekers and Splash Walls can both impede incoming enemies and assist allies pushing into enemy territory. Short-ranged weapon users must instead make use of the side paths between the three middle corridors to dodge out of the enemy's line of sight. These paths are also a great spot to ambush enemy players. If you have Beakons, hide them within the nooks and crannies around the center to give your team a good staging ground.
A lot of battling will involve fighting around right-angled corners which tends to favor defenders hiding behind them. Make liberal use of your bombs if you need to flush them out. Exclusive to this mode are the two vehicles which are wide enough to completely block off one of the pathways when it moves. They can serve as cover from enemy fire, or as a vantage point to get high ground on an otherwise flat battlefield. They also let you get on top of the shipping crates facing the wide rectangular court, which attackers can use to bombard foes with their subweapons or suppress foes using Chargers, Splatlings or ranged Shooters.
Wrestling control of the enemy team's rectangular lot is difficult but can secure a victory if you succeed. The enemy team has a lot of space to hide or maneuver around an attacking force, with deep corners to ambush any foes moving in. It is difficult for one player to defend two paths at once, so having a minor numbers advantage on the attacking side is a good time to push. Completely inking out at multiple corridors lets your team attack from different directions, but watch out for stealthy foes using the other paths to encroach from behind. The pathways aren't long at all, so a failed push can give the enemy team an opportunity for their own push.
The battle is as good as over once one team controls the other side's lot, as the deep corners now work against the losing team trying to leave spawn. Unless the attacking team has pushed right to the spawn point, the higher paths surrounding the middle courtyard should remain exclusive to the losing team, but they are low enough to be pressured by stray fire and bombs.
Splat Zones
There are two splat zones, one of each at the left corner of either team's clearing. The barriers from Turf War are carried over here.
The strategy for Splat Zones is very similar to Turf War. You have an almost identical map and your goal is the same: push into the enemy team's court while keeping yours protected. However, the position of the zones cause an interesting change in how the three lanes down the middle are used. From the perspective of your team's zone, the left lane is the closest path to your own zone, so it requires the most protection from enemies. Similarly, your right lane is the fastest route to the enemy's zone, but you'll encounter the most resistance. The middle lane is more neutral in purpose, acting as an alternate route for either team's offense.
Even though there is no map objectives at the center grid in this mode, it remains the most important part of the map to control. Monitor all three lanes for enemy activity, and always attempt to push forward down the lanes into enemy territory. Long-range weapons and Splash Walls are still incredible for deterring attackers, while short-ranged weapons have speed and the element of surprise to both attack the enemy zone and pick off the enemy offense. Pushing out multiple lanes at once will give you the best chance of capturing the enemy zone as you can approach it from different directions.
The zones themselves are not very large, typically an Inkstrike is enough to make it neutral and a Sprinkler can cover much of its area. While you can make use of the corner of the zone to surprise attackers, it is generally a bad idea to fight directly on the zone itself. For defenders, position yourself to the right of the zone so that you can ink it when necessary, as well as respond to incoming foes from all three lanes. For attackers, coordinate your attacks and specials to get the best chance of claiming the enemy zone. A lightning offensive combined with an Inkstrike can give you enough momentum to take it.
Due to the nature of dual zone maps, both teams tend to be equally tied, so the smallest lead can take a long time to surmount. The layout of this map in particular means that you can't quickly switch from attacking the enemy zone to defending your own, so you must really commit to your chosen task.
Tower Control
Due to the mostly flat terrain of the map, the tower is roughly half the height it is in other maps. It is located at the center of the stage and leaves the central grid through the middle path. It then turns left and goes down the enemy's right path from spawn. After that, it makes two more right angle turns to switch to the opposite path, ending its journey by ascending up the container in front of spawn. An inkable wall has been added below the left flank route to assist in the push into enemy territory.
The 100-80 range is where the tower will spend its time most of the match. The tower fits snugly in the middle of the intersection between paths, providing cover and blocking vision against any enemies on the other side. Getting on the tower is dangerous since the short height means that enemies can easily nick you. Try to take control of one of the side routes and flank foes from there or take control of the entire grid to be able to push out. If you don't completely secure the central area, the tower is potentially vulnerable to attack from up to 3 directions, incredibly hard for people on the tower to survive. Splash Walls are especially useful here, as the tower will pass through the wall but enemies will be blocked.
The next big hurdle is the wide clearing. The tower is still very vulnerable to enemies attacking from multiple directions. Watch out for the left ledge where the tower enters the enemy hallways, as foes can get the drop on you here. This section of the path is another stalemate-likely area, and is the ideal spot for the defending team to stop the push. There is plenty of space to maneuver around enemies, while chargers and splatlings can snipe foes off from the flank routes. This increased space also helps the attackers, as they can spread out and engage the enemy team with more visual coordination.
Once the tower enters the hallway, it is now possible for players to jump on to the flank route from the tower. This final stretch is still difficult to push through as the defenders can come from the sides or above, but it also places immense pressure on the defending team. The ability for enemies to get on the flank routes gives the attackers a lot of momentum to push, and can keep the defending team from sneaking around the tower and attacking from behind. For close matches, the tower will rarely get to the goal, but the battle is all but concluded once it reaches the 10s.
Rainmaker
The Rainmaker spawns at the center of the grid. The goal is on the container in front of spawn, which can be climbed up using a steep ramp. An inkable wall has been added to the middle-left route from spawn.
Like in most maps, the Rainmaker starts at the center of the map, but the claustrophobic layout of Port Mackerel creates a unique dynamic during the opening skirmish. Since it can only be shot at from four narrow directions owing to the crates, bursting the Rainmaker's shield comes down to which team has the superior firepower. Most players will be concentrated in the center lane, as the side lane is a tad exposed to the enemy team for just bursting the bubble shield. Therefore, it is harder to pick off individual foes focused on the shield during the starting phase as an ambushing player will have to face the brunt of the enemy team at once, but a successful ambush can result in a massacre.
Without a significant number advantage, getting the Rainmaker out of the grid will be no easy task. The Rainmaker's charged shots are amazing for forcing foes out of the entire lane, but there are many corners and openings that let sneaky foes pick off the carrier. Once the Rainmaker is dropped, it is also difficult to reclaim it since the shield can block out entire junctions when expanding, severely limiting your movement around the Rainmaker when bursting the shield. The bubble also obstructs your view of enemies on the other side.
Pushing through the court isn't easy either if it has been thoroughly covered by enemy ink. The Rainmaker is much less effective here as there is more space to evade its shots, but it is very handy for taking out snipers perched on the higher walkways. The open space gives the defenders more chances to get around and behind the carrier, or cut off the Rainmaker carrier's ink path from the side. You must have a coordinated attack to make it through this area, and it's where an evenly-matched battle usually stalemates at.
Pushing past the 60 mark is difficult and typically means you've already won if you succeed. The Rainmaker is once again a deadly threat due to the narrow, straight corridors, and with only two lanes there's less space for opponents to hide when the Rainmaker pushes in. However, the defenders do have the high paths on the sides to attack from above, or even behind the attacking team. The attackers can get on to high path using the metal blocks, but it is risky to do so due to the proximity to the enemy spawn. The 20 point mark is nearly unpassable due to the steep ramp to get on to the goal, but is effectively a victory if you can get to that point.