Casting Shadows is an ability for Night Cap in Plants vs. Zombies: Battle for Neighborville. It creates a shadow dome that hides ally plants, slows down enemies inside the dome as well as inverting their controls.
Hide allies and restrict enemy movement in the shadow dome.
Casting Shadows can be used to trap Zombies, restricting their movement and lowering their accuracy, making them an easier target. This allows you to easily vanquish them with Spore Strike or finish them off with Fung Fu.
Casting Shadows is also a useful tool for reviving allies. Enemies won't know what to shoot at, so you can revive a fallen comrade without having to worry about being hit. Watch out for the Engineer if trying this strategy, as his splash damage will hit you even if he can't see you.
Another good way to use Casting Shadows is to escape a large group without getting hurt. Shadow Sneak could be used for this, but enemies will know that you're trying to escape and may try to look for the cloud of smoke that you leave behind when you move. Instead, use a Casting Shadows, go inside of it, then enemies will think that you're tying to stay and fight. However, this is the time to use Shadow Sneak, retreat in another direction, and you're opponent(s) won't pay attention to the smoke you leave as they'll be focused on attacking the Casting Shadows. Again, watch out for Engineers.
The Engineer, as mentioned earlier, is good at attacking any enemies hiding within a Casting Shadows. Using his Heavy Helper, he can repeatedly spam his Concrete Launcher to do massive damage to anyone inside. Using Bullhorn Swarm prevents any Plants from escaping your trap.