Change your preferences here.
Deals damage. If the target's HP is at 50% or less, the Base Power of the move doubles.
Brine may be exceedingly powerful when the opponent has less than 50% health, but generally the move will have a lower damage output than Surf and Hydro Pump. When the opponent is at less than 50% health, one of these moves would often KO, and should the opponent switch to a healthy Pokemon, Brine would likely do pathetic damage. However, there is certainly scope for its use on an inventive set; for example, a Walrein in Hail could use Super Fang in combination with Brine to take down opponents with a swift one-two punch, with no need for any attacking investment. However, it is recommended that you stick to more reliable moves.
Surf is a more powerful and reliable alternative with no added effect.
Scald is a more powerful and reliable alternative that may inflict a burn on the opponent.
Hydro Pump is a far more powerful alternative with lower accuracy.