Most skins are tied to specific achievements, such as: Beating certain boss encounters. Completing the game on various difficulty settings. Earning "Par" times on levels.
You have a limited number of "lives" or "retries." If you run out before finishing the final world, the run ends, and you must start from the very beginning [1]. tinertia-codex-update-v2-0-gauntlet-mode-and-skins
Familiarize yourself with the end-of-level portals to maintain your speed as you spawn into the next stage. Most skins are tied to specific achievements, such
Complete every level in the game (over 70 stages) in a single, continuous run [1]. the run ends
You can change your skin in the Main Menu or the Pause Menu under the "Customization" or "Codex" tab.