Gameplay Mechanics Design
The way the players interact with your game makes them want to play it. Gameplay mechanics are much more than just a set of Left/Right/Up/Down controls. It is the most essential part of game design and literally includes the description and operation of every parameter, defined throughout the game, be it a number of lives or magic spells or weapons upgrades. Every modern game with the possible exceptions in Hyper-Casual Style contains multiple secondary game mechanics in addition to the core one. The challenge here is to make everything players do in the game make sense and fit well with each other. I.e. if game’s core mechanics is a shooting single enemies, adding empire building as a secondary one might not be a good fit due to different scales. Creating mechanics which is equally deep requires experience, so it is better to hire a game designer to back you up.