Gems will always spawn at the edge of pits. When they are on the same side as you are, wait until the last possible moment to jump on them. If the gems are immediately after the gap, you can jump earlier than usual to make sure you will not miss them. At times you will find a single spike or zombie hand in front of you, immediately after a drop. Do not attempt try jump over them, as this is a trap to get you to lose a life on another obstacle just ahead. To get past this situation, let Mounty fall off the ledge and he will land just after the obstacle. You will then be ready to jump over the second obstacle.