Bastion

From BoardGameGeek:

The castle is besieged! Hordes of monsters gather near the ancient walls and are about to smash open the castle gates. Mountain giants trample the fields, fire riders burn the surrounding settlements, and the ice dragon has nested on top of the citadel tower, horrifying the minds of the inhabitants of the bastion. Only a squad of stubborn heroes stands between the enemies and their ultimate victory. Bastion is a cooperative castle defense game set in the Berserk universe, with 1 to 4 players taking on the roles of magical castle defenders. The castle is located in the center of the game board and is menaced by a great variety of invading enemies: dangerous beasts, ferocious warriors, terrible monsters, giants, mages, and even mighty dragons. You will travel the bastion districts, draw energy from sources of magic, build obelisks, bombard the enemies by magical devices and learn new spells. You will be gathering specific mana that is required to defeat each of the invaders. Victories allow castle defenders to gain new abilities, build powerful artifacts, and perform magic rituals. To defeat a monster you usually must travel to its location and spend a specific amount of mana of a required color. Each defeated monster provides you with a new spell. The tougher the defeated enemy, the better spell you will get. Castle defenders should try to be as efficient as possible. If you take too many actions to defeat your threats, the bastion will fall. Bastion is a cooperative adventure: you either defend the city by concerted efforts or it will fall under the pressure of the attacking hordes. Bastion is a highly customizable and replayable game. There are several scenarios and difficulty settings in the rules, along with the solo mode.