Almost all duelists use a boring and annoying monster whose effect is extremely hated and loved: Ally of Justice - Catastor.
The effect is quite simple and it annoying if he Battle against a monster whose attribute is not dark, it automatically destroys the monster without damage calculation.
I'll talk about how to avoid losing monsters on the field to that effect. About the possible ways to combat and probable strategies to overcome Catastor.
Let's start with another irritant: Wind Up Zenmaines. If we manage to field a Zenmaines before our opponent summone the Catastor, we have a slight advantage, but this does not indicate that we can not summons him after our opponent has a Catastor field. Just remember that any card on the field can be cleared by the conditional effect Zenmaines. So if your opponent tries to destroy his Zenmanies with the effect of Catastor, simply apply the effect of Zenmaines. However, remember that to activate the effect at End Phase, the Zenmaines must be in the field.
If you are fan of Blue-Eyes White Dragons, a more viable solution is the use of Blue-Eyes Shinning Dragon. The only but it is only able to summons him. One tip is to use the field spell Fusion Gate. But only in extreme cases (the dragons you have at hand to summon the Blue-Eyes Ultimate Dragon, but where is Polymerization? Whether you have the Fusion Gate on Terraforming and hands or her deck, you're done).
But why use a dragon so hard to summon? Simple, he can not be targeted by effects, traps and spells. Thus, the effect of Catastor against him worthless.
Finally, the most practical way is to use traps like Mirror Force, Magic Cylinder, Negate Attack and any other trap that serves to counter attack. Since the effect of Catastor need a Damage Step and to obtain this he needs a Battle Phase and attack if you use Mirror Force, besides destroying a catastor even destroy the monsters in attack mode on your opponent if you use a Magic Cylinder, your opponent will take damage and use Negate attack, he also loses the Battle Phase, giving you the chance to strike back and even turn the duel.
Well, this issue does not end here, and come back soon to talk about it. Any questions, post here what I shall answer.