You begin with RuneScape gold five available block slots,but this number increases as you progress in the game. Once you earn 300 quest points,you'll unlock a sixth slot,and by completing the Lumbridge Elite Diary,you'll open a seventh. The Quest Cape is an excellent goal to aim for when you're serious about Slayer,as it also provides many useful rewards. Diaries can significantly improve your stats and provide valuable XP,so it's worth the effort.

For this guide,I will assume you have access to all seven block slots and that you are using Duradel as your Slayer Master of choice (or Kuradel,if you've completed While Guthix Sleeps). The monsters listed here are based on the general inefficiency and low XP returns associated with them. The order isn't important,as different players may find certain monsters more annoying than others.
1. Hellhounds

Hellhounds are often seen as a great AFK option due to their low combat requirements. However,when it comes to XP efficiency,they fall short. Although their Slayer Boss,Cerberus,drops valuable items like the Primordial Crystal,the task itself can be tedious and offer poor XP. The lack of good drops (other than the occasional clue scroll or Ensouled Head) makes Hellhounds a poor choice for efficient training.

Given their single-target nature,these monsters aren't suited for multi-target spells or cannoning. As such,they should be blocked if you're looking to maximize your XP per hour.
2. Cave Krakens

Cave Krakens are another high-weight,slow XP monster that you'll encounter frequently. They have a high Slayer task weight,so they show up often,and their drop table is unimpressive. You can only kill them with cheap OSRS gold magic (typically a Trident of the Swamp),which slows down the process.