False Prophets, Deceptive Teachers, Destructive Doctrines
Bible Verses which declare the serious nature of false prophets, false teachers & destructive doctrines:

I John 4:1-3
1)   Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world.
2)   By this you know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God,
3)   and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of the Antichrist, which you have heard was coming, and is now already in the world.

2 Peter 2:1-2
1)   But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction.
2)   And many will follow their destructive ways, because of whom the way of truth will be blasphemed.

1 Peter 5:8
8)   Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour.

2 Timothy 3:1-7
1)   But know this, that in the last days perilous times will come:
2)   For men will be lovers of themselves, lovers of money, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy,
3)   unloving, unforgiving, slanderers, without self-control, brutal, despisers of good,
4)   traitors, headstrong, haughty, lovers of pleasure rather than lovers of God,
5)   having a form of godliness but denying its power. And from such people turn away!
6)   For of this sort are those who creep into households and make captives of gullible women loaded down with sins, led away by various lusts,
7)   always learning and never able to come to the knowledge of the truth.