Hi GM!
Fierce countenance translates exactly as "stern faced", indicating that it is his (FACE), and not just his mood. It is translated precisely as{of fierce}"az"{countenance}"paniym". Therefore it is his "Mighty" appearance which will add to his deception as God in the flesh, in addition to his cunning speech. In addition to sharing the Gospel, we are to "test the spirits" 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.
The Spirit gives assurance(And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us. 1 John 3:24) But how are we to know if it is Gods Spirit? and not a lying one who is assuring them? Christians must be wary that they are not misled, therefore their doctrine must be aligned with what the scriptures teach. Likewise with the person planting the seed, unless it is planted with the "Good Seed" and not the type that will bring forth "tares", it must be rooted out. One tare can bring for a harvest of tares, the tares{zizanion} "darnel" are false converts which can produce a substantial amount of counterfeits, the difference? the wheat comes to fruition and brings forth fruits, the darnels do not. And any tree that does not bring forth good fruit is cast into the fire, fruits not only refer to attitude but the doctrines they proclaim as well, which is why every believer must "Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth." By diligently studying the word of God in addition to "applying" the to our lives, we are then able to discern truth from falsehood. Just by looking within some of the threads on this board, I have come across doctrines that are to be found (NOWHERE) within Scripture, you might have come across it on another thread and they can be very deceiving, just be careful thats all.
Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world. (John 4:1)
Take Care and God Bless!