The third game type is called Sandbox, which gives you infinite resources and lets you start and stop enemy attacks whenever you want. This game type is great once you learn the basics, letting you experiment with strategies you can use in the other two game types.
To add even more options, there's also a crafting section where you can modify and upgrade walls, turrets, and weapons using resources mined in the game.
Block Fortress, on its surface, seems to have it all. It has the look and block-building mechanics of Minecraft; open-field tower defense elements with upgradeable turrets; and lets you play it like a first-person shooter once the action begins. But even with all these positives, you have so many options and upgrades the game feels almost too complicated for its own good.
Still, Block Fortress will definitely appeal to people who don't mind getting down and dirty with the game's multitude of options and upgrades. If you like the idea of playing a game that mixes three game genres, and don't mind a learning curve to really get going, Block Fortress is a unique option.