Achieving level 99 Slayer in Old School RuneScape is one of RuneScape gold the most grueling,time-consuming feats in the game. Those who have reached this prestigious milestone understand just how vital managing your Slayer Block List is for efficiency. 

The journey requires a staggering 13,034,431 experience points,and it's a grind that takes years for most players. However,99 Slayer is typically not something you grind specifically—it's a natural outcome of training your combat stats. Slayer,after all,is more of a supplementary skill that enhances your combat experience rather than something you actively focus on.

To make the journey a little smoother,players have the option to block certain Slayer tasks,which can help avoid frustrating monsters and slow XP gains. By spending 100 Slayer reward points at a Slayer Master,you can block up to five monsters from appearing on your tasks.

 Unlocking additional slots is possible,with the sixth slot becoming available after reaching 300 quest points and the seventh slot unlocked after completing the Lumbridge Elite Diary. Having six to seven slots open can be immensely helpful for those who are serious about grinding out Slayer,and acquiring the Quest Cape should be a priority for players planning to spend a lot of time in OSRS.

For the sake of this guide,I'll assume that you have unlocked all seven block slots and are using Duradel as your Slayer Master (or Kuradel if you've completed the While Guthix Sleeps quest). Below is a list of some of the most annoying and inefficient Slayer tasks that you might want to block to maximize your XP gains.
Hellhounds

Hellhounds are a common Slayer task,but are not efficient for XP training. Although they offer decent AFK opportunities and a few valuable drops like the Primordial Crystal,their slow kill times mean you won't make fast progress towards 99 Slayer. Hellhounds also have a very poor drop table—outside of the occasional clue scroll,Ensouled Head,or rare Smoldering Stone,you won't make much money off these tasks. They can become especially frustrating if you're after the best possible XP per hour.
Cave Krakens

Like Hellhounds,Cave Krakens are also high-weight tasks that appear frequently,but they don't provide the best XP rates. These monsters are weak to magic,so you'll need to use a Trident of the Swamp or similar single-target magic weapon to kill them. The process is slow,and their drop table is underwhelming,meaning you won't earn much GP while completing the task. Given their high Slayer task weight,Cave Krakens are perfect candidates for your block list if you're aiming for a more efficient Slayer grind.
Black Dragons

While Black Dragons can be profitable due to their dragon bones (good for Prayer XP),they are not ideal for efficient Slayer training. These creatures have high Hitpoints and require you to bring either an Anti-Dragonfire Shield or an Antifire Potion,adding extra prep time to each task. For maximum efficiency,you'll need to use a Dragon Hunter Lance,which is expensive and generally reserved just for Slayer tasks. Since Duradel assigns a relatively low number of Black Dragons to kill per task (around 10-20),it's better to block them and focus on monsters that can be killed in bulk for RuneScape gold for sale greater XP gains.