Fog

[izik99]

After my opponent declares attackers, can i cast {Fog} rendering the attack useless? Same for other fog effects?

[izik99]

Sure. All damage is prevented, so long as it's cast before the Combat Damage step.

Can i declare blockers, so they think im not casting one, and after they pump thier creatures with something then cast fog, so they waste a spell?

[Ghebert]

Yes. You gain priority during he combat damage step before the damage is done and after the declaration of blockers.