Being inked causes characters to take more damage proportional to the coverage amount. To achieve this, there is a damage multiplier that is calculated with 1 + ink * 0.5 / 180. With this equation, the maximum damage multiplier of 1.5× is reached when the character is covered by 180 units. Characters can be covered by up to 300 units of ink, and each individual attack has its own ink cost and the coverage amount. The ink will also gradually deteriorate over time, with the time roughly being 2 minutes.
Inkling's tank holds 150 units of ammunition, although these units are not to be confused with units of coverage. These units of ammunition are instead used for Ink Cost. For example, Inkling's neutral infinite will take 2 units of ink from the tank per hit, which will cover the opponent in 10 units of ink per hit. As a result of this, 18 hits of Inkling's neutral infinite will cover the opponent in 180 units of ink, thereby reaching the 1.5x damage multiplier cap.
The color of ink does not matter, aside from potentially making the coverage amount harder to estimate. An Inkling is also equally affected by having their own ink reflected at them, which can technically make it worse for the player should this occur. When Kirby copies an Inkling, he will use the first color of ink that isn't being used by another character, whether that be an Inkling or another Kirby. Master Hand uses a light blue ink. Some Assist Trophies can also be covered in ink.
The stage can also be covered in ink, which reduces the moving speed and jump height of opponents while they are touching it. This is an additional property of a specific move, Splat Roller, rather than a side bonus of ink attacks themselves. The effect on jump height has unintended interactions with certain momentum-based moves, such as increasing their height.
In addition to the above, attacks may have the ink effect, which produces specific graphics on hit. This is entirely independent of the ink mechanic.
List of ink attacks
In addition, all of Inkling's floor attacks have the ink effect, without applying the ink mechanic.
By enemies and bosses