Mob Attributes are a huge part of minecraft because with out them mobs wouldn't give you the challenge you face today in survival mode.
These today are one of the most customized things for map makers.
Now this blog will finally teach you how to customize them without any external tools or mods.
Things you need:
Minecraft 1.7.2
basic knowledge about commands and command blocks
basic knowledge about mobs

Now here is a list of attributes:
generic.maxHealth
generic.attackDamage
generic.knockbackResistance
generic.movementSpeed
generic.followRange
zombie.spawnReinforcements
horse.jumpStrength

These are self-explanatory enough
Now to use this just add this data tag:
[Attributes:[{Name:attribute name,Base:amount}]}
In the place of attribute name put there the name of the attribute you want.
In amount put the amount you want, remember that it cannot exceed 0 and 999999

If you've noticed that in 2 of the attributes mentioned above that 1 says zombie and the other says horse instead of generic
this means that this is exclusive to 1 mob type.

If you've ever been on minecraft gamepedia then you'll know that you can actually add attributes to items.
But I already created a post for that go check it out if you want to know how!

This just was a simple blog post on how to do this later on i'll be making a complete tutorial on how to create a sucessful map.

Leave a diamond if this really helped you out.