The coin/gem is in a hidden room behind a black wall that you can walk through behind your spawn point.
After saving the Female Survivor, she confesses that her schoolmates went through a portal, and she woke the Dragon. Then, the dragon sent monsters to the worlds, and they are passing through the Desert to get to the dragon's Island. It is unknown on what happened to the 2 school boys.
Do not get too close, as the monsters will hit you.
Kill the monsters as quickly as possible, since you earn a star by killing monsters quickly. Do not rush it, though.
Use pets, as a minor/major backup for killing.
Follow the green arrow that appears once there are 5 enemies left, in order to kill the enemies quicker.
Restore your ammunition by aiming for the head. This method is also useful for killing monsters quicker.
Use Armor. If you have a decent amount of armor, you will not have to worry about getting damaged, because you can get 3 stars even if you have damaged armor. This doesn't apply to Health.
The enemies aren't extremely tough in this level, so you can equip the weapons with a decent amount of damage.
Verify if there are enemies behind you, in order to save yourself from ambushing enemies.
When fighting the boss, aim for the red spot. This is the boss's weak spot, and it will only take damage if you shoot the boss at it.
In this case, use an accurate weapon like the Nail Minigun. However, do not spray and pray too long, as you will lose accuracy overtime, and its bullets will be wasted.
In the desert part, there seems to be sand having an animation of moving water, which is quicksand. Before, this area simply had an invisible border. Now, you can enter here, but damage will be taken. You will not sink or move slower when you enter the quicksand but you will die instantly.
There is a glitch that occurs if you are on top of the head of the Sphinx statue in that all the monsters, rather than just the Pharaoh Golem, will be able to climb to the very top and get you. This glitch still remains unfixed.
In the 10.6.0 update. The Pharaoh Stalker was replaced by the Pharaoh Golem.
The old Sphinx's face looks like a Creeper's face from Minecraft.