The brackish blade is a one-handed weapon that requires 60 attack to wield. It is dropped by 'Rum'-pumped crabs in the Braindeath Island 'Rum'-geon that is unlocked in the quest A Clockwork Syringe. It has a higher stab bonus than Korasi's sword, but a lower strength bonus. Unlike other popular stabbing weapons such as the Zamorakian spear and Korasi's sword, the Brackish blade has an aggressive stab stance. This weapon is equal in all stats to a Dragon scimitar (including attack speed), however the stab and slash stats are switched, and it has 1 less slash defence. Korasi's sword and Chaotic weapons are harder to obtain and have higher requirements to equip, this weapon is of great use to players fighting monsters weak to stab, such as dragons. This weapon does not need the quest to be completed, or even started, to use.
The weapon, along with the Brine sabre, also deals more damage and is more accurate against the 'Rum'-pumped crabs, and is able to hit even higher than the chaotic rapier. Occasionally while fighting them a message appears saying "The brackish blade seems super-effective."
The Brackish blade has a special attack, 'Rum'ify. It doubles the chance of hitting, and adds 2.5% of the damage dealt to your Strength, Attack and Defence, draining 75% of the special attack meter. If the target is low on health and the hit is fatal, even with low damage, the player's stats will still be boosted according to what the hit would have been. This special attack visibly boosts stats and does not stack with the effects of potions or any other boosts. It is also worth noting that the special attack reduces the maximum damage capable for that hit.
Brackish is a term used to describe water which is a mix of fresh water and salt water.
A player will (most of the time) either deal a maximum hit or no damage when its special attack is used; it's not known whether this is a glitch or not.
The special attack is influenced by prayers like Ultimate Strength. Before using the special attack it is strongly recommended to turn on a strength prayer.
The Brackish blade is often used as a substitute for a dragon scimitar for training strength.
It is also highly favoured to use when killing dragons, as most dragons are weak against stab attacks.
The quote "The brackish blade seems super-effective." may be a reference to Pokémon.
Despite the Brackish blade's strong offensive bonus to stab and weak offensive bonus to slash attacks, the weapon's powerful special attack is portrayed as a downward vertical slash.
The special attack seems to be unaffected by the effects of the salve amulet, so if using the special attack against undead purely for the stat boosts, it would be wise to switch to a different amulet for the attack.