Hellhounds in SoulSplit are considered the best NPC/Monster to kill when hunting (hard) Clue Scrolls. They have the highest number of killed to number of clues out of any other monster. They also drop an assortment of herblore secondary, and all farming herb and tree seeds. They can be located in Taverly Dungeon in the very back (North-West of the spawn location if you have high enough agility). (The dungeon can be reached by Dungeon Teleports > Last page > Taverly Dungeon)