Hellhounds are one of the first monsters that highlight a common theme across this list—single-target tasks are less efficient than multi-target ones. To RuneScape gold maximize XP per hour,it's better to focus on monsters you can use a cannon or area-of-effect spells like Ice Burst or Ice Barrage on. Hellhounds are relatively slow to kill and drop few valuable items,mostly dropping low-value items such as clues,Ensouled Heads,or the rare Smoldering Stone. Despite their potential for AFK gameplay and the decent drops from their boss,the experience per kill is underwhelming compared to faster,multi-target alternatives.
Like Hellhounds,Cave Krakens have a high Slayer task weight,meaning they're a frequent assignment that you'll want to avoid. These monsters also can't be killed using melee or ranged combat,limiting you to using a Trident of the Swamp or other single-target magic weapons. Their drop table is also lacking,with few valuable items to offset the slower kills. For these reasons,Cave Krakens are a prime candidate for your Block List,as they take considerable time to kill while offering minimal rewards.
Black Dragons are another task that may seem like a good challenge,but ultimately is slow and inefficient. Not only do they have high hitpoints,but you'll need either an Anti-Dragonfire shield or an Antifire Potion to protect yourself from their devastating breath attack. While you can earn Dragon Bones for Prayer XP,they also have high defenses and require expensive equipment like the Dragon Hunter Lance for optimal kills. Plus,Duradel typically assigns only 10-20 of these dragons,which isn't ideal since you're aiming to kill large groups of monsters to maximize XP per task.
Both Greater Demons and Black Demons should be blocked for similar reasons—high Slayer task weight,poor loot table,and inefficient XP. Duradel assigns large quantities of these monsters (typically 130-200),meaning you'll be stuck killing them for long stretches of time without gaining significant XP. Moreover,these tasks can be frustrating since you often have to compete with other players for kills,leading to slower kills and wasted time. While these demons can be useful for buy RS gold Ironman accounts due to their shared Demon classification (allowing for the use of the Slayer Helm),for most players,the inefficiency of these tasks makes them a poor choice for leveling Slayer.