Puzzle Quest 3

You can get this by playing the main story.

Make sure to keep upgrading your equipment and magic and your gear rating
will always be above that of your enemies.

Once your hero reaches Level 8, Autoplay is unlocked, meaning you can just enter a level, turn on Autoplay and let your hero do the work for you. So the last couple levels will be a breeze.

I unlocked this half way through Chapter 3. So you should unlock it around that point as well.