Answer:

The first question is very easy, the second question is hard to give a hard and fast answer. 

Obviously, the Bible absolutely condemns every and all forms of witchcraft.  Numerous scriptures can be used to make this point.  Galatians 5:20 comes to mind.  Sorcery (which is a synonym for witchcraft) and witchcraft are condemned again and again throughout the Old Testament and then again in the New Testament. (examples:  Leviticus 19:26, Deuteronomy 18:10, Acts 19:19, Exodus 22:18, Micah 5:12, 2 Kings 9:22).

Can a person be the victim of witchcraft?  For this one, the Bible does not really give us a completely clear cut answer.  Some will say that all this witchcraft and sorcery is a lot of superstition–that it is completely fake.  If witchcraft is really all just a delusion, then obviously no one can really be bewitched.  I wish the answer to your question was that simple.  So is there "legitimate" witchcraft?  In other words, can those who practice the "black" arts actually do something?  Can they use the power of Satan to actually cause something to happen?  Some will use the case of the magicians in Egypt in the time of Moses as an example.  Scholars debate whether what they did was mere trickery or a demonstration of some real power to work the miraculous.  Others will mention the witch of Endor (1 Samuel 28) who may have used sorcery to bring up the spirit of Samuel.  Again, many will debate that this woman had any real power.  Another relevant passage is 2 Thessalonians 2:9 which tells us that false teachings will be accompanied by counterfeit miracles which are the work of Satan.  Again, are these real miracles done by the power of Satan or are they bogus "miracles" inspired by Satan to distract us.  Is witchcraft real?  I have my own opinion, but I will let you reach your own conclusion.  I will say that in many countries outside the West, belief in real power, Satanic or otherwise, is nearly universal.  You will not succeed in convincing those from these countries that witchcraft is not real. 

If you conclude that witchcraft may have some actual power, then the question comes up; what should I do about it?  My answer is you should do nothing!!!  Satan is the one who wants you to focus in on witchcraft and those who practice it.  My suggestion is to simply rely on God to protect you from such things.  Do not give Satan a foothold by giving your attention to such things.  God will take care of you.  Trust in him.   Ephesians 6:10-18 and Romans 8:37-39 teach that we must put our trust in God about such matters.  He will not let you be dragged away or lose your salvation if you simply trust in him.

I do not know what you are referring to in your third question.  It sounds like you have heard of some sort of superstition about invoking the blood of Jesus to defeat a demon.  I would advise you to not give any credence to superstitious mumbo jumbo about invoking the blood of Jesus to defeat a demon.  There is no support for this in scripture.

John Oakes