1 - Right behind from where you start the level, there is a miniature cannon biomech, kill it.
2 - Behind the stairs leading to the first wooden lift, there is a kamikaze doing some weird stuff, kill it.
3 - In the village section, behind the house that has the portal in it, there are a couple of armor shads that lead to a single pill, grab it.
4 - In the village section, there is an invincibility powerup on top of the house that has the portal.
5 - In the village section, there is a house that appears not to have a door. You need to do some platforming to enter through the door located on the outside.
6 - After killing all enemies in the laser rifle fight, you will be able to swim through the water. There is a portal under the water on the opposite side of the waterfall.
7 - The Mental Stronghold: The key to enter is located underwater in the small lake of the foggy section. The entrance portal is on the left path of the foggy section, in between some rock, hard to miss. Beat the Mental Stronghold to fulfill the secret.
8 - After killing all enemies from the last wave by the cave with the skull, after 5 seconds the skull's eyes will light on fire, shoot the skull.