4x4 Crystalline Defense

There are 16 cells on the playing field. Clicking on a cell deletes its contents.
At the same time, both positive and negative images are deleted. After a certain period of time,
they are replaced with new ones. The effects of images that have not been removed are applied to the player.
Clicking on the blue crystal during the game adds 3 health points to the player. Clicking on the red crystal during the game closes all the pictures.
The game is played until the player reaches the 999 difficulty level, or up to zero health points.
The difficulty level affects the time when new images appear.