Mark 13:21 And then if any man shall say to you, Lo, here is Christ; or, lo, he is there; believe him not:
Mark, by the Holy Spirit placed this earlier in the chapter, he repeats this again, so it is important.
Mark 13:5 And Jesus answering them began to say, Take heed lest any man deceive you:
Mark 13:6 For many shall come in my name, saying, I am Christ; and shall deceive many.
Mark 13:22 For false Christs and false prophets shall rise, and shall show signs and wonders, to seduce, if it were possible, even the elect.
Satan will raise up false Christ's, false leaders with miracles by sorcery; by calling upon a lying spirit. The elect have God's Spirit, so they should not be deceived. Some will be immature, not studying God's word or following Jesus, the Good Shepherd. These could be deceived along with the world's people.
Mark 13:23 But take ye heed: behold, I have foretold you all things.
Take heed, remember and prepare. You need not be taken by surprise.
Luke 21:8 And he said, Take heed that ye be not deceived: for many shall come in my name, saying, I am Christ; and the time draweth near: go ye not therefore after them.
This no time to be spiritually asleep. Be awake and discerning of what you hear. Don't follow anyone who cannot be tested by the Spirit and the word.
1 John 4:1 Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
They are clever deceivers. It may come down to whether or not you feel God's peace in their presence. The Holy Spirit is what brings us together in unity and in peace. If they sound "way out there," leave them.