Each night a merchant arrives to sell you upgrades for any Gems and Coins you've gathered from your ancestors. You then have the chance to dig up a few more, and can then click to place your initial units. Each unit has their own special abilities, such as Farmers who can plant apple trees enabling you to afford more units. Take notice, in some levels you'll need to keep Farmers on the board if you're going to be able to keep shoring up your numbers! Felling foes will often net you rewards like Gems, Coins and Stars. A unit's skills will charge whenever that unit type attacks the baddies, resulting in Stars that afford uses of their special abilities at the left by clicking on them. For some of them, you'll need to then pick a target location on the field with another click. The levels start off fairly easy, but watch out for a difficulty curve that spikes near the mid-game and becomes suddenly unmanageable for the last level. Though some of the 22 levels can get a bit grindy and take plenty of retries to get right, the playability's enough to make that experience enjoyable. Mostly! A Fast Forward feature would be nice for some of it, but it's useful to know that you can usually return to the menu with the Gems and Coins you've garnered so far and try again with some improved capabilities.