25 game comes from Bart Bonte. I'm a big fan of his games.  This particular game is a point scoring game that is very similar to some other, more famous games.  Threes came out about 5 years ago. (It was immediately cloned and renamed as 2048 about a hundred times.)
Looking at the images if 25 game, I was prepared to hate it, for being another clone.  However, after playing it 6 or 7 times I love it.

The rules:
1. Combine two 1's to form a single 2.  Two 2's form a single 3. Etc.
2. You run out of room when the grid fills up.
3. After each swipe, in any direction, a new tile will emerge, either a 1 or a red tile.
4. Red tiles: this is what makes the game so unique because they're annoying, but also useful.
5. Red tiles will vanish when 3 are lined up. 6. Scoring: There is no significant reward for merging two 9's over two 5's.

Like the game Threes, there is an addictive quality.  My high score is 21,573. My highest tile was 11.  The game took just about an hour.

What could be better:
1. Threes has better graphics. The part I like most is the ability to swipe very slowly without making a commitment. This lets one see which tiles will merge.
2. There needs to be a leaderboard.  If my high score is not in the top 1%, then I'm going to continue to play. 
https://apps.apple.com/us/app/25-game/id847466186
https://play.google.com/store/apps/details"id=air.air.A25

Other Bart Puzzles:What's Inside the Box"Factory Balls ...