*Only dropped by Bloodvelds in Zamorak's Fortress. ^Only dropped by Bloodvelds in the GWD (including Zamorak's Fortress.)
These Bloodvelds are stronger than those found in the Slayer Tower, more difficult to access and with the exception of Zamorak items, have the same drops. There are also not a lot of them grouped together so killing them for a Slayer task is not efficient and not recommended.
If you do wish to fight them, then remember that you must have God items or Shard of Zaros equipped to prevent the monsters in the dungeon attacking you.