How one design rule makes a Sudoku-2048 hybrid actually work

A developer has built Number Merge Sudoku, a puzzle game that merges mechanics from Sudoku and 2048 on a shared grid. The core design challenge was reconciling 2048's need for duplicate tiles with Sudoku's uniqueness rule, solved by introducing two tile states: 'material' tiles can merge freely and are exempt from Sudoku checks, while 'locked' tiles are committed as Sudoku digits and cannot merge. Players spawn material 1s, merge them to build higher values, then seal tiles to lock them into the Sudoku layer — a win requires every cell to be locked with each digit appearing exactly once per row, column, and box. Difficulty scales through board size, undo budget, and hint count rather than pre-filled givens, with Easy on a 4×4 grid and Medium and Hard on a 6×6 grid. The game also allows 'soft-lock' dead ends, which the developer intentionally preserved as a meaningful risk arising from managing a merge economy under a uniqueness constraint.