Left/Right mouse button - Add/Remove tiles
Z - Clear screen
X - Place random tiles
⬅️/➡️ - Switch tile set

Marching Squares is an algorithm that places different sprites based on the number of surrounding neighbour tiles.

For tile based level design this algorithm can really be a huge boost in efficiency. It works fast even when evaluating all tiles per frame which means this can easily be incorporated into procedural generation methods with relative ease.