Why do Atheists call God the Almighty magical and a sky fairy ?

Ridicule is the last gasp of the defeated.

mag·ic

/ˈmajik/

noun

noun: magic

    the power of apparently influencing the course of events by using mysterious or supernatural forces.

Sounds like your sky daddy to me...

HEY LOOK EVERYONE, FIREBALL IS COMING OUT ATHEIST. ANSWERING QUESTIONS FOR ATHEISTS MEANS YOU ARE AN ATHEIST IF YOU ANSWER IT FIREBALL. WE SHOULD ALL WELCOME OUR NEWEST MEMBER TO THE ATHEIST RELIGION. WELCOME FIREBALL.

God is omnipotent and a person can know this with certainty by reciting the rosary of the Virgin Mary every day with care and sincerity.

Because that's basically what it is.  By magic, I mean anything supernatural.  You believe God has magical powers that can reshape reality in any way despite that violating just about every law of physics.  That's magic.  You're defining 'magic' very narrowly.  I'm not.

Sky is in there because he's in heaven, and heaven typically is associated with puffy clouds and what not.

And fairy, because fairies are a broad classification of magical beings.  I didn't say God was female, and nothing about fairies implies femininity.  Though, to be honest, the power of CREATION really is a more feminine trait than a masculine one.   But fairies include a wide range of magical make believe creatures. 

Sure, the description of "magical sky fairy" is uncharitable, and not ENTIRELY accurate...but it's not entirely INACCURATE either.  I use the term at times to drive home the point that God is a childish make believe creature with no evidence for his existence...just like magic and just like fairies.

Why do Christians call Allah a "pagan moon god" when you have to do some serious distorting of historical background to get that result?

Some do use these names for gods because they know it annoys some theists. 

As for magic, atheists do not believe in gods. To them the supernatural power gods use is no different to that of any other fictional beings and the generic name for that power is 'magic'. 

You guy throw a fit every time we call him a fairy tale, Fable, Myth, Fantasy, Delusion, Superstitious Bullsh!t , Imaginary , Worthless Invisible Friend,  Etc.

We were just being polite

Good point . My key word is Skydaddy 

but i see i need to change that to  Transcenddaddy .

 Should i spell that with one d or two d's ?

 Or 3 d's or 4 .

The answer to your question:  Because atheists, by definition, do not believe in the existence of God.  And some of them are rude & mean.  Have a great day!