Does God lie? And does the devil tell the truth?

I don't know denominational or traditional perspectives, but God didn't deceive or mislead Eve. Eve lacked faith in God. She did in fact die on that day; whether it was a spiritual death (probably more likely how God meant it), or her body started the decaying process and died in a day in the eyes of God (as mentioned by BigM).

We (or at least I) am not at liberty to say when lying is okay, even if you think it will save someone's life (not necessarily saying I wouldn't do so..), because, in a sense, it might also lack faith.

The bible does not teach us to lie and scare our children into obeying and behaving. They should just obey and, if appropriate, tell them the truth of why in a way that they can understand. The bible teaches us to discipline our children (moderately) to obey and behave.

Foolishness is bound up in the heart of a child, but the rod of discipline will drive it far from him.
Prov. 22:15

Withhold not discipline from the child; for if you strike and punish him with the [reedlike] rod, he will not die.
Prov. 23:13

The rod and reproof give wisdom, but a child left undisciplined brings his mother to shame.
Prov. 29:15

In those verses the devil told them they would have the knowledge of good and evil, which was true. Also a demon tells the truth of Jesus' identity in Mark 1:24

What have You to do with us, Jesus of Nazareth? Have You come to destroy us? I know who You are—the Holy One of God!

"Now the devil tells Eve that she will not die and that she will gain the knowledge of good and evil. Which happens from what the Bible describes."

So Eve is still alive today? She is not, she died thousands of years ago, despite the devil claiming she and Adam would not die.

They both did, so the devil lied. I find it hilarious how certain people go to great lengths to try to spin that God lied, whle it is clear that the devil DID lie, and yet they still claim he did not.

Adam and Eve spiritually died that day - the moment they sinned and forfeited their holy status before God.

Rejecting God's fellowship is just as equivalent and awful as death.

That's the whole point of Christianity. To be born again and make dead men alive through the grace of Jesus Christ.

John 3:1-21

3 Now there was a man of the Pharisees named Nicodemus, a ruler of the Jews. 2 This man came to Jesus[a] by night and said to him, “Rabbi, we know that you are a teacher come from God, for no one can do these signs that you do unless God is with him.” 3 Jesus answered him, “Truly, truly, I say to you, unless one is born again[b] he cannot see the kingdom of God.” 4 Nicodemus said to him, “How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?” 5 Jesus answered, “Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. 6 That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.[c] 7 Do not marvel that I said to you, ‘You[d] must be born again.’ 8 The wind[e] blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.”

Ephesians 2:4-5

But because of His great love for us, God, who is rich in mercy, 5 made us alive with Christ, even when we were dead in our trespasses. It is by grace you have been saved.

Without the blood of Jesus Christ, we are really just walking pieces of flesh. Even worse, this flesh once had honour and prestige yet all of it was forfeited, to lust after lowly garbage. Just like Esau.

I think two scriptures will answer your question for you:-

1

NWT Titus 1:1, 2 "Paul, a slave of God and an apostle of Jesus Christ according to the faith of God’s chosen ones and the accurate knowledge of the truth that is according to godly devotion 2 and is based on a hope of the everlasting life that God, who cannot lie, promised long ago;..."

2

NWT John 8:44 "You are from your father the Devil, and you wish to do the desires of your father. That one was a murderer when he began, and he did not stand fast in the truth, because truth is NOT in him. When he speaks the lie, he speaks according to his own disposition, because he is a liar and the father of the lie.

God cannot lie and Satan cannot tell the truth.

The first scripture that comes to mind is that God cannot lie nor can he repent (i.e. change) (Num 23:19). The next one that comes to mind is that Satan has no truth in him (Jn 8:44).

Finally, though it is less accepted, they did in fact die in the day they sinned because God's time is much different than ours (2Pe 3:8). One thing to note to support the aforementioned notion is that no man has lived to see 1,000 years. The oldest man in The Bible, Methuselah, lived to be 969 years old. (Gen 5:27)

God cannot lie: Numbers 23:19, Titus 1:2, Heb 6:18

The first link is the word of God directly given to Balaam who was summoned by the king of Moab out of fear regarding the encampment of Jews near them and the possibility of war with them.

The second is written by the apostle Paul in the preamble to his epistle to Titus.

The third is from body of Paul's epistle to the Hebrews.

All are direct and unequivocal in their statements that plainly God does not lie.

The fact that God knows all truth and does not lie is a bedrock foundation for Christians. Our own faulty processes of reason and emotion which help us understand the world around us but through which we can make mistakes in our understanding because of our own limitations even though we are led by the Holy Spirit in our lifelong search to understand and follow the truth of God's word is a human quality. The fact that we lie is a human quality. God should not be seen through the lense of these two fallibilities of humans.

God knows all truth and knows all the world and the universe he created from their beginning to their end. And, unlike our own fallibility, God is infallible and not only has the capability to never lie to us but according to these clear declarations simply does not.

If God were to lie to us it would water down his message and make the truth as revealed to us by him confusing to grasp and we would always be wondering - did God lie about that? What was the truth from God, and what was a lie?

We can know with comfort and peace that God has and will always speak the truth to us. It is from this bedrock foundation of knowledge of the absolute truth of the revelation of God that we can indeed have infant-like faith in his Word. That faith is indeed the ultimate foundation not only of our relationship with God but of our very salvation through Christ.

We can also take comfort in his promises, or covenants, with us. We can know that the promise to Noah as symbolized by the rainbow to never again send a flood to destroy most of the world would be honored as long as this temporal universe exists. We can know that the covenant with Abraham that his people would become numerous as the sands and be a blessing to all nations will never be broken by God.

Most importantly we can know that his free gift to us of salvation by grace through faith in Jesus Christ, taken as our Lord and Savior which leads to eternal life in Heaven, is a pure and absolute gift with no possibility of withdrawal by God for anything we might do, however bad (except the one exceptional sin of blaspheming the Holy Spirit).