Make Power Ups Compatible with and Complimentary to the Player Character
Designing a character and their specific power-ups and upgrade systems usually takes a lot of refinement and adjustment to get just right so don’t be discouraged if you hit a few brick walls and some power-ups or upgrades just don’t work out or make the cut. The first step is to make sure that every power-up gives the player an ability or boost that makes sense for the character. You want the power-ups to be compatible with the character’s normal attacks, movements and metrics. There are some universal abilities that work in almost any game like extra strength, speed and durability. Then there are other more interesting power-ups that are character specific, level specific or even enemy-specific in some cases that add variety without being cheesy.
Imagine a character’s ship in a space shooter getting a power-up to disable other ships with an EMP. That power can change the gameplay immediately and fits in logically with who the player character is and their normal abilities. Some characters allow for more possibilities and combinations than others. How about a growing and shrinking power-up or a power to reverse bullets using magnets for a sci-fi character from the future? They have future technology and would logically be able to bend the rules and do things out of the ordinary right? If the power-up makes sense for the specific character and the specific world you’re building then use it.
Your power-up can also be a permanent character upgrade or item to use in specific situations. How about an underwater breathing mechanism like air bubbles for an adventuring character that can swim in caves? Later you can acquire an upgrade to unlock an underwater breathing device that eliminates air bubbles. Similar upgrades can take the place of or enhance normal abilities. Power-ups should be used as temporary means to complete a specific task or function.