At the beginning,you'll have five available slots on RuneScape gold your Block List. After earning 300 quest points,you can unlock a sixth slot,and after completing the Lumbridge Elite Diary,a seventh slot will open up. By the time you hit this point,you should already be working toward obtaining the Quest Cape,as it's crucial for long-term progress in OSRS. The various diaries in the game also provide valuable rewards and experience,which makes them worth pursuing.

Now,let's dive into the monsters you should consider blocking for the best XP gains. For this guide,I'll assume you have all seven slots open and that you are using Duradel as your Slayer Master (or Kuradel if you've completed the "While Guthix Sleeps" quest). The following recommendations are in no particular order.
Hellhounds

Hellhounds are among the first monsters that should be considered for blocking. While these creatures are decent for AFK training and have some valuable drops like the Primordial Crystal,their XP gains are slow. Hellhounds are single-target monsters,meaning that they don't offer the multi-target opportunities that would help you maximize your XP. This can make grinding through OSRS gold for sale a Hellhound task incredibly time-consuming.