If the Devil punishes people, aren't he and God on the same side?

If you say the Devil punishes people, do you mean that he causes people to suffer? Because he definitely does. On the other hand, God has allowed people to make the choice to serve him which doesn't bring punishment. Or to serve themselves or the Devil's interest, which sooner or later leads to harm or punishment.

So I agree that it would make no sense for God and the Devil to work together as would be the case with hellfire punishment.

No because God doesn't punish.

Look, if the concept of God includes Him being Omniscient (Which it does MANY times throughout the Bible) and God is Omnipotent (again, throughout the Bible) then how would Lucifer had fallen if not be God's Plan? 

Well it would be right in line with God creating Evil (Isaiah 45:7) and God needing an agent to bring the "idea" of Free Will to Eve and Adam. If God saw those two first humans (via Omniscience) grab and eat the forbidden fruit, certain integral parts had to be in play for this to come to fruition... 

So since God NEEDED Lucifer to be that medium of evil on earth and provide the façade of "Choice"...Why not set Lucifer up for the "Fall"?

In this way Lucifer really would be working for God, as a predestined agent of evil to facilitate God's Perfect Plan for mankind.

Hang on there, Mr Majinn, you've got the bull by the horns.

It is God who makes the rules, God who judges, God who metes out the sentences. The poor old Devil is only the turnkey. He's a victim of the system, just like the rest of us.

Omar had a more optimistic view. He put it this way:

O thou who didst with pitfall and with gin
Beset the road I was to wander in;
Thou wilt not with enchantment round enmesh
Me, and impute my fall to sin.

As a couple of believers may have pointed out, the Bible doesn't actually mention that. Believe me, I grew up thinking the same thing. The Bible actually says that Satan will be tormented along with the sinners in Hell.