Most of the little Metroid details that can be found within Metroid: Negative Mission.
I really wanted to capture the Metroid feel and a lot of that came with the design of the stage itself, but some of it has to do with the many references I crammed into the stage. Players trying to rush through might miss many of these references. So here is a list of little Easter eggs, some of which are more hidden than the rest.
1. You are playing as Samus almost the entire time. Some players were mad and thought I included too many Mystery Mushrooms, but I did this for two reasons. First, wanted people to play as Samus, and second, I wanted players to see the entire stage. If I took some Mystery Mushrooms out there would be some very annoying segments and players may not feel like Samus if they are forced to play as Mario for long amounts of time.
2. I tried to make it clear at the end of the game by writing it out in coins, but there are 15 hidden 1-Ups to find in this stage. I like to think of them as E-Tanks. So if you're looking for more of a challenge try to collect them all in one run.
3. You can see Samus's ship at the start of the mission.
4. A Chozo statue is holding Samus's suit.
5. The famous Screw Attack image can be seen at a few points drawn out in blocks and coins.
6. The vine-climbing segment is meant to represent Samus's wall jump.
7. The bosses are meant to resemble Kraid, Ridley, and Mother Brain.
8. Many of the rooms and ways to get 1-Ups (E-Tanks) are based on places they'd be in the NES Metroid.
9. The space animals from Super Metroid make appearances and can be saved at the end of the game. (The Goomba's are the Etecoons and the Green Koopa Troopa is the Dachora.)
10. When Samus gets the Star Power at the end it's meant to be like when she uses her Speed Boost ability.
11. Super players will be able to finish the adventure with the Zero Suit.
There are even more than this, so happy hunting. Also continue on to see a complete spoiler filled cheat guide for this adventure.