If you find a path with no obstacles, it probably doesn't lead anywhere.
There's nothing worse than an empty level you just walk through, so we need to start throwing things in the player's way. Good things, bad things, things that make the player cry with pleasure and weep with sadness. We need mechanics. Lucky for us, there are four types of these beauties to work with: mechanics, hazards, props, and puzzles.
Before we dig in, be aware that mechanics is another term that suffers from MDS: multiple definition syndrome. Board game designers say mechanics are the gameplay systems used to play a game. These are things like turns, action points, resource management, bidding, and even rolling the dice.
Video game mechanics are objects that create gameplay when the player interacts with them. They can be jumped on, activated with a button press, or pushed around. Combine them with interesting level layouts and enemies. Some of the more common video game mechanics include:
Switches and levers
Platforms are a beloved mechanic of action game designers. They come in a wide variety of styles and flavors that can be used to bedevil and delight players. Here's a suitable-for-framing chart that I've devised to help you identify platforms in the wild. Be careful, some of them bite!
You would think that something like doors would be easy to design; after all, ...