How to make flying mob that gonna shoot fireballs or enderballs, or mob that gonna teleport sometimes like enderman

To make the mob shoot projectiles there is a box for that in the AI tab while making a mob. You can't customise the projectile much though

To make it randomly teleport, you could make a procedure which happens every tick and looks like this:

If NOT is provided world client :

-If (get entity nbt variable <teleportcooldown>) > 100:

--Set <local:teleportx> to [(Random × 10) - 5] + x

--Set <local:teleporty> to [(Random × 10) - 5] + y

--Set <local:teleportz> to [(Random × 10) - 5] + z

---If (is air at <local:teleport x>, <local:teleporty>, <local:teleportz>) AND (is air at <local: teleportx>, (<local:teleporty> + 1), <local: teleportz>)

----Teleport entity to <local:teleportx>,<local:teleporty>,<local:teleportz>

----Set entity nbt variable <teleportcooldown> to 0

-Else:

      Set entity nbt variable <teleportcooldown> to (get entity nbt variable <teleportcooldown>) + [round(Random × 4)]

I know it's kinda messy but it took a while to be written XD

No problem!

Anyway, I forgot to say you should also check if the block under the teleport destination is not air