Tibet
The boss in Tibet is the yeti. To defeat him, dodge the rocks that the Yeti throws at you. When you get to the bridge, the Yeti will try to throw the rocks at your head. Duck them, run at the Yeti, and you will scare him away. You can now grab the treasure.
Egypt
In Egypt you have to face a giant crocodile. To defeat him, all you have to do is jump over all of the tiles while he chases you. As long as you don't let him catch you, he will eventually run out of energy and you can claim the treasure.
Africa
In Africa you have to defeat a giant snake. To do so, first go through the maze of the snake's body. At the end is the snake's head. When you get to it, the snake will move, allowing you to gather the treasure.
Babylon
In Babylon, you have to face a Venus flytrap. Go through the various smaller flytraps before you get to the giant one. Dodge the seeds that the flytrap will spit at you. When you are allowed, go through the side of the flytrap and collect the treasure.