During the Dark Ages the Catholic church presented the idea of Satan and his followers being red with pointy tails, pitchforks and two horns on their heads. They were made to look as scary as possible. Further, they were presented as being there to roast people over a raging fire. Yet what do the Scriptures tell us?
"And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, And prevailed not; neither was their place found any more in heaven. And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceives the whole world: he was cast out into the earth, and his angels were cast out with him." Revelation 12:7-9
So here we have Satan leading his group of "angels". And we have Michael (an angel of God) leading his group of "angels". So whatever an "angel" looks like both must be the same. Can we imagine that God's angels are red with pitchforks etc.? I don't think so. These angels appeared to servants of God throughout the ages.
Then we have the conversation where Satan appears to Moses after the Lord did _
"Blessed be the name of my God, for his Spirit has not altogether withdrawn from me, or else where is your glory, for it is darkness to me? And I can judge between you and God; for God said to me: Worship God, for him only shall you serve." Moses 1:15
So here we have Moses saying that Satan's glory is darkness instead of light.
Further understanding comes from the following verses _
"And now, when Moses had said these words, Satan cried with a loud voice, and ranted upon the earth, and commanded, saying: I am the Only Begotten, worship me. And it came to pass that Moses began to fear exceedingly; and as he began to fear, he saw the bitterness of hell. Nevertheless, calling upon God, he received strength, and he commanded, saying: Depart from me, Satan, for this one God only will I worship, which is the God of glory." Moses 1:19-20
A couple of things stand out here. Firstly I was brought up to believe that Satan was intelligent. But here we have Satan throwing a tantrum and thudding the ground because he can't get his way. But also note that because Moses then began to fear that Satan suddenly had power over him. It wasn't until he called upon God to help him that Satan's power over him ended. So Satan's power over us can only be felt if we turn to lust, anger, hatred, fear, greed and any of those darkside feelings.
Matthew quotes Christ on 3 occasions saying how that wicked church members will be cast into "outer darkness" (Matt 8:12, 22:13, 25:30) in the final judgement. Yet Christ also refers to "hell" as being like a fire that all the wicked must suffer. Alma points out that this is just a way to explain it and that it is only "as" a lake of fire and brimstone; there is no real fire (Alma 12:17).
This helps us understand why Christ refers to people having to suffer a fire and yet be in darkness. It also tosses out the concept of red devils in fire.
So what does Satan look like? He looks like any other spirit. He has two arms and two legs etc. The difference is that although you can see his spirit body's matter, all is darkness around and through him. His thinking is totally distorted and he seeks evil continually. He is miserable but certainly would argue otherwise. His only power is that which comes from your incorrect emotions (as we see from the Moses incident).