Defeating most enemies and Bosses
Circle around the enemy or Boss by pressing either Left on both Analog-sticks or Right on both Analog-sticks. This will make you surround the enemy or boss while keeping your view on it. Then, shoot them with any weapon. If it flies press Right Analog-stick Down slightly, so you can watch it while it flies.

Birdskulls
To get the ten Birdskulls, you must first have the assassin's rifle. After getting the assault rifle, go to the beginning of the path that leads you to Netti's church. You will see a hut. Turn right and you should see another hut that has/had a Cadeaux in it. Go around it and you will see lots of barrels. Back up slightly and shoot them from a safe distance with the assassin's rifle. A path will open. Follow the path until you reach a lake with birds flying around and a few crocodiles. Kill the crocodiles before going any further. The birds flying around carry the Birdskulls (one each). Kill ten of them. Note: One of the birds only flies around once in a while so it is difficulty to kill it. Every bird that you kill in this area will drop a birdskull into the water. You must swim to get it. The birdskulls never disappear. In the event that they drop one on a boat, forget about it -- you cannot go on top of them. If this happens the game will send an extra bird.

Nephilim Shard
The Nephilim Shard is given to you by Duncan the first time you see him; immediately after you find Jaunty and the ten bird skulls.

Hint: Control loading screen:
Rotate the Left Analog-stick or Right Analog-stick at the loading screen to make the words and the fire in the background move around.

Hint: Shadow Gun and watch:
You find the Shadow Gun and Mike's watch in the sepulcher, which is where Duncan sends you. It takes a while until you get there.