Many parents find that just helping their children find words to describe their fears can ease anxiety. Give him a break. Forcing your child to pet a dog or to sleep without a nightlight won't ease his fear. At this age, he's probably better off conquering his fears at his own pace. Use your imagination.
Laughter goes a long way toward diffusing anxiety.
But you can keep this flashlight here to scare away the pretend monsters. Until your child outgrows his fears, do whatever it takes to provide reassurance. For example, if your toddler won't take a bath because he thinks he'll get sucked down the drain, let him sit on a plastic chair in the tub. Give him a special washcloth and let him clean himself with a shower attachment. If your child tends to get nervous in large gatherings or new situations, he'll probably do better if you tell him what to expect.