A little number that might be sung by Magneto's followers. Set well before X3 (obviously), most likely circa X1.

A Mutant Rallying Song
(tune: "The Times, They Are A-Changin'")

Come gather 'round, mutants, for this much we know
When humans are frightened, to war they will go
And we must be ready to strike the first blow
We'll use all our powers wide-rangin'
Though the humans may struggle, they never can win
For their own children are changin'

They think they can hold us at bay with their guns
They would murder their daughters and slaughter their sons
But we are the stronger, the chosen, the ones
And theirs is the species that's agin'
So if we survive this round, we'll carry the day
For their own children are changin'

If you think we should pity them, don't be a fool
For humans are petty and brutal and cruel
First we will conquer them, then we will rule
No matter that they may be ragin'
And then they'll be gone and the world will be ours
For their own children are changin'