123456 is a puzzle game that is solely based on computer characters and its composed of one mechanic only: clicking.
Scenes consist in a grid of multiple tiles having these show a character. The initial state of these tiles is configured during Unity edit-mode.
For fast and consistent structure between scenes, a small tool was created so the tile grid would be easily created and modified during edit-mode.
For the majority of puzzles a single script manages the puzzle state, its behavior and its win conditions.
Other considerations for defining puzzle behavior were LUA script implementation and component-based behavior. The latter one was used until puzzles started to get more extravagant.