The black magic is specially performed by TANTRIK a person who perform activities which are not useful or not in the benefit of the organization. He can kill someone or even he can kill some kid in womb or hurt someone and make him alive again only in that case if the dead body is not burnt.
He can ruin someone business and his life. Although he can perform these tasks but such tasks are not fruitful. Performing such task only add worries in the TANTRIK life. The tantric usually use the tool KEELNI, because sometime it happens that the negative powers which he sends towards a person and if that person has used some protection then these powers fire back on the tantric. So to protect yourself from own negative powers the TANTRIK uses tool KEELNI.