Bloodveld are Slayer monsters requiring level 50 Slayer to kill. They have similar drops to Lesser demons. Aside from Slayer tasks, bloodvelds are sometimes killed for their favourable green charm drop rate, otherwise they are rarely killed offhand.
The God Wars Dungeon is usually not a recommended place to kill Bloodvelds. There are not enough to support a player, and are fairly spread out throughout the rooms except in the Zamorak Fortress entrance area. You also need God-related items to protect yourself from them and other monsters. Other than that, it may be a fair choice to kill the ones near the entrance. There are always Spiritual warriors and Spiritual mages killing Zamorakians there. The ones located here are weak to Water spells. The nearest bank is in Burthorpe.
The Slayer Tower is a popular choice for those who have not completed Legacy of Seergaze. There are several Bloodveld spawns on the first floor of the tower, in the south-west corner. It's often crowded, so try to find a server where they are not overcrowded to kill them. The nearest bank is Canifis. Bloodvelds here cannot be cannoned.
Although Bloodveld are weak to thrown weapons, if you get them as a slayer task and ask Duradel or Kuradal for tips, they will claim that fire spells work well against them (which is true for Mutated Bloodveld but not others).
This is strange, as Bloodveld are Chthonian and Zamorak led the Avernic demons in an uprising against the Chthonians. It could be that the Bloodveld betrayed the other Chthonians and followed Zamorak because they, like the Avernic, were kept as slaves and/or pets (much like the way vampires now keep them).
Bloodveld are one of the only two types of demon to drop bones rather than ashes, the other being hellhounds.
The examine text of bloodveld is very similar to the examine text of the dust devil, basilisk, and rockslug. The bloodveld is "the tongue of evil", the dust devil is "the vacuumed face of evil", the basilisk is "the eyes of evil" and the rockslug "the slime of evil."
The bloodveld seems to attack twice in a row but it only attacks once, as seen on the hitsplats.