Ok so yesterday me and my friend came up with this way to kill fangspawns. No video, just pictures.
With this method my friend, lvl 35 archer killed em in about 7 mins and each gives him 160k xp which gives more than 1mil exp /hour.
Just to clarify, you pull him up on cliff, you stand near edge of cliff, wait for him to do his jump then you jump down and start shooting him, you have to be under him, otherwise he will reg hp.