Thermal Ink

Thermal Ink is an ability in Splatoon 2.

Thermal Ink reveals the location of players that the user deals damage to with the user's main weapon as a 'direct hit' (meaning that indirect Blaster blasts or indirect hits from a Sloshing Machine or Explosher do not count in this case), for about 16 seconds. Tagged players are revealed via a white silhouette, only to the user and only while at least 150 DU away from the tagged player (Bomb Defense Up DX increases this minimum distance) and only while the tagged player is not submerged in ink.

Tactics
Thermal Ink tends to be useful with main weapons (especially long range) that tend to hit opponents but not quite splat them, such as the Jet Squelcher. Thermal Ink tends to not be useful with main weapons that splat opponents quickly, such as the Sploosh-o-matic.