Greater Demons and Black Demons are high-weight Slayer tasks that require a lot of effort for RuneScape gold minimal reward. These demons are single-target monsters,which means your kills will be slow,and their loot table is less than impressive. Duradel frequently assigns these monsters in large quantities,often around 130-200 per task. 

The XP from these demons doesn't make the grind worth it,and if you're trying to maximize efficiency,these tasks should be blocked as well. For Ironman players,these demons might be useful for the Slayer Helm and other specific items,but even so,the slow kill rates make them better left off your task list.
Spiritual Creatures

Spiritual Creatures found in the God Wars Dungeon (GWD) are some of the most frustrating Slayer tasks in the game. These monsters don't have a particularly high task weight,but they are extremely tedious to kill. They drop poor loot,and getting to the GWD in the first place is a hassle. 

Without wearing specific God Wars Dungeon gear,you'll be constantly attacked by other monsters,which is an added annoyance. The task is already time-consuming,and the rewards just don't justify the effort. Unless you're specifically hunting for Dragon Boots or want to test your patience,this is a task that should remain blocked.
Steel Dragons

Steel Dragons are notorious for their difficulty and slow kill time. Like Black Dragons,they have a strong dragonfire attack,meaning you'll need either an anti-dragonfire shield or an antifire potion,along with Protect from Melee prayers to mitigate their damage. While they can be killed with Earth Spells after the Project Rebalance update,it doesn't significantly speed up the process. 

The task request is usually small,but Steel Dragons hit hard and are tanky,so even though they don't take long to kill individually,they become a chore over time. Their drop table is subpar,and with buy Runescape gold their high defense stats,you'll find yourself getting very little XP from this task. Therefore,Steel Dragons are best placed on the Block List.