death_black_drake_02 is currently unused because of a typo in the soundevent file (game_sounds_creeps.vsndevts)

Also, while I'm at it, the Prowler ancient creeps have no death sounds and no footstep sounds currently. All other neutral creeps do havea both. They could use these as death sounds

death_dragonspawn_sorcerer_01
death_dragonspawn_sorcerer_02

death_dragonspawn_overseer

And for footstep sounds, they should use "n_creep_Hooved.Footstep", since they are hooved creatures.