Splatoon/Sub-weapons and specials

Other than your primary weapon, you also have access to a sub-weapon, which uses up a lot of ink but usually has a significant effect, as well as a special, powerful tools that can only be used after inking enough turf. The sub-weapon and special you get is always tied to your main weapon, so even weapons that share the same stats can require different playstyles depending on the sub-weapon they have.

Sub-weapons
Sub-weapons mostly consist of powerful thrown grenades or helpful support items. They typically use up a lot of ink, so they can't be spammed carelessly. The ink pack on your back will glow whenever you have enough ink to use your sub-weapon, serving as a useful visual indicator.

Splat Bomb
Splat Bombs behave like standard grenades: they explode a while after being thrown to deal heavy damage and spread ink in its blast radius. The bomb has a short fuse which only counts down when the Splat Bomb touches a solid surface like a wall or floor. Splat Bombs are versatile and can be used to cover areas outside your reach, such as enemies beyond your main weapon's range or around corners. They are also good for map control by forcing foes out of strategic positions. You can control when the bomb explodes based on the way you throw it. For example, rolling a Splat Bomb along the ground or off the ledge activates its fuse earlier, causing it to explode faster than a tossed Splat Bomb at the cost of range.
 * Ink cost: 80%
 * Damage: 180 (decreases with distance from the center of blast)

Burst Bomb
Burst Bombs deal a fraction of a Splat Bomb's damage for a fraction of the ink required. Since it uses up so little ink, it is very spammable and is often used more like an alternate main weapon than a backup. Burst Bombs explode immediately, which limits their use to direct combat, although they can also be used to quickly cover a patch of turf for weapons that can't do so. Burst Bombs kill in 2 direct hits or 3 indirect hits, so you can take on foes in mid-close range engagements exclusively using Burst Bombs. Burst Bombs are usually utilized to make up for a main weapon's weaknesses. On short ranged weapons like the Carbon Roller, it's used to attack foes that are out-of-reach; on long-ranged weapons like the E-liter 3K, they are close-range defenses against flanking or surprise attacks.
 * Ink cost: 25%
 * Damage: 60 (Direct impact, lower damage if hit with splash)

Suction Bomb
Suction Bombs have suction cups that attach to any floor, wall or ceiling they touch. They have the same damage and blast radius as Splat Bombs but a slightly longer fuse. Suction Bombs have the similar uses to the Splat Bomb, only with improved ability to deal area pressure. Since they take longer to explode, they also scare foes away longer, letting you restrict their movement more effectively. Conversely, it is also harder to splat enemies as they have more time to react and escape before the bomb blows up. Fortunately, being able to stick Suction Bombs lets you use it more unpredictably, such as by attaching a Suction Bomb on the wall around the corner to catch foes rounding the bend.
 * Ink cost: 70%
 * Damage: 180 (decreases with distance from the center of blast)

Seeker
Seekers are small boats that slowly travel forward, leaving a trail of ink behind. They can move up ramps, and will explode upon hitting a wall or enemy. Seekers has minor homing capabilities against enemies, but they cannot detect any foes hiding in their ink. Seekers move slowly and can be avoided by entering squid form or simply jumping over them, but their ink trail and interaction with terrain make them interesting explosives. Seekers can carve ink paths through neutral or enemy territory, helping you hurry to your objective or approach a targeted enemy. They are most effective on long, straight corridors as they can move their max distance uninterrupted and cover the corridor efficiently. You can use a Seeker's behavior to your advantage, such as by sending them off ledges or up ramps to surprise enemies.
 * Ink cost: 80%
 * Damage: 180 (decreases with distance from the center of blast)

Ink Mine
Ink Mines cannot be thrown, only set on the ground near you. Once set, the Ink Mine will activate and explode if an enemy gets close, the surrounding area is covered by enemy ink, or after a certain amount of time has passed. You cannot place another mine until the previous mine explodes. Ink Mines are Suction Bombs taken to the extreme. They are really good at stage control, being able to lie dormant for roughly 10 seconds and driving off foes that set them off, but they are utterly ineffective at splatting enemies. The mine glows brightly for a moment before exploding, giving a small window for foes to react to it, so good Ink Mine placement is necessary to make them a considerable threat. Small, actively contested spaces are the best candidates, with the most common being the tower in Tower Control.
 * Ink cost: 60%
 * Damage: 180 (decreases with distance from the center of blast)

Disruptor
Disruptors are thrown like Burst Bombs, but instead of dealing damage, they coat all foes caught in the blast radius with a debuffing liquid. Foes under the effects of a Disruptor debuff experience drastically reduced walk speed, swim speed, jump height, ink recovery and become visible to enemies even when swimming in their own ink. Even though it doesn't directly hurt opponents, the Disruptor is a powerful support tool that cripples the fighting abilities of enemies, ruining their mobility and making them easy prey for the user and teammates. Their relatively cheap ink cost lets you spam it somewhat, which is useful for scouting out areas or pressuring foes.
 * Ink cost: 50%

Point Sensor
Point Sensors function similarly to Disruptors, but instead of debuffs, they mark the position of enemies within the blast for all teammates to see. The Point Sensor is a smaller-scale version of the more commonly seen Echolocator special. While its effects are minor compared to other thrown sub-weapons, it can be very helpful if you mark the right enemy. The Point Sensor has a low ink cost, so you can fling several into enemy territory to detect any potential ambushes. Generally, you can ignore long-range attackers like Chargers that can shrug off the effects by keeping themselves safe through sheer distance. Instead, go for mobile or stealthy flankers like Splash-o-matics or Rollers as they rely heavily on the element of surprise to get kills.
 * Ink cost: 40%

Sprinkler
Sprinklers can be attached to any solid surface, after which they will start spreading ink indefinitely, two drops at a time while slowly rotating. Only one Sprinkler can be on the map for each player, using another one causes the previous to disappear. The Sprinkler is purely a support tool used to both claim turf and harass enemies. They can ink a surprisingly large area given enough time, and leaving a Sprinkler to ink up your base can net you a big chunk of your special meter. Sprinklers have about the same health as players, so they serve as moderately effective distractions in enemy territory, although it uses too much ink for direct combat. The best Sprinkler placements can ink contested spots while being hard to destroy. Typically, these positions are angled on walls, behind corners and sometimes even on low ceilings.
 * Ink cost: 80%
 * Damage: 30 per drop

Splash Wall
Splash Walls are thrown a short distance ahead before activating, creating a temporary ink barrier that blocks all of your shots, but allows your own shots to pass through. Enemies that pass through the wall are instantly splatted, but they can attack the Splash Wall to reduce its duration, and there can only be one Splash Wall per player active at any given time. Splash Walls are commonly given to long-range weapons like the .96 Gal and Splatling, their purpose being an additional line of defense. Splash Walls block all shots from one direction, letting you fire at foes with impunity. Splash Walls can also be placed to your sides to ward off enemy flanks while you focus on another direction.
 * Ink cost: 60%

Squid Beakon
Placing a Squid Beakon creates a super jump spot that can be used only once. Up to three Squid Beakons can be placed on the map per player, each of them visible to both teammates and enemies. Squid Beakons are purely supportive items, and how useful they are depends on the locations they're placed in. Since you can already super jump to any living teammates and the spawn point, it is best to leave them in hidden, low traffic areas with quick access to the frontlines. Since enemies can see the position of Squid Beakons on the minimap, you really need to hide them well. Squid Beakons are very helpful for difficult sieges or pushes, transporting fallen teammates to the battlefield quickly even in the event of a major loss. They can also sometimes serve as distractions since enemies would want to get rid of them quickly, setting them up for an ambush.
 * Ink cost: 80%

Specials
On the top-right corner of the screen is your special bar. It will slowly fill up when you ink turf, and lets you unleash a powerful special when it is fully charged. You will briefly shine and your Inkling's hair will start flaming once you get your special, visual cues visible to both friend and foe. Dying will take a large chunk off of your special bar, so make sure to survive when you have a special until the right moment to use it.