The majority of level elements only feature one level of interplay. Properly designed enemies, like the ones I detail below, work with the level elements to develop higher levels of interplay. Even in my previous examples, I couldn't help but mention a few enemies because they're so closely intertwined with the level design.

 

 

The Goomba is a classic Mario enemy. Though the Goomba isn't the simplest enemy in Super Mario Brothers due to its level 2 interplay (which I will explain shortly), it is the most basic enemy that makes up the foundation of the enemy design. After all, that lone Goomba is the first enemy encounter in 1-1.

 

As a simple minded fungus, the Goomba travels slowly in one direction. When a Goomba comes across a wall or other non hostile solid object, it simply reverses direction. Overcoming a Gooma is as simple as waiting for them to walk themselves to their doom, jumping over them, jumping on them, hitting a brick they're standing on from underneath, throwing a fireball, or kicking a koopa shell at them. But don't be fooled.

Depending on a variety of factors, Goombas can become a deceptively effective enemy. Fireballs can bounce over their heads. If you're big Mario attacking Goombas from underneath, the bricks can break creating an opportunity for the next Goomba to land right on top of you. And if you think you can squish the first Goomba and relax, the next Goomba in line can reverse direction off of the squished remains. These level 2 interplay designs make the Goomba a formidable enemy depending on their numbers and level position.

And if you think the Koopas are another simple enemy, consider that the Para-Koopa can reach up to the 7th level of interplay.

1. De-wing the Para-Koopa by jumping on it
2. The Koopa will fall to one side and walk in Mario's direction upon landing.
3. Green Koopas generally walk themselves to their doom unlike Red Koopas who turn around on the edges of platforms. In order to attack the Koopa, it must be jumped on or bumped from underneath. Unlike the Goomba, there is no way to kill a Koopa by just jumping on it or bumping it.
4. Once the Koopa has been attacked, it'll rest in its shell. But after approximately 5.5 seconds, it'll wake back up. What's even trickier is, depending on the Koopa, upon waking, it'll head in Mario's direction even if it wasn't moving in Mario direction before.
5. To prevent the Koopa from getting back up, it can be kicked away while still inside its shell. This is also useful as an attack against other enemies.
6. If the shell hits a solid level element, it'll bounce back toward Mario. This sliding shell poses a threat.
7. To avoid getting hurt, there are only a few courses of action. One can always simply jump over the shell. However, to counter it directly, Mario can stop the shell from moving by jumping on top of it, or kick another shell into it for a double KO. If Mario stops the shell, then the cycle resets back to level 5. If it ever wakes up again, the cycle resets back to level 3.