Proper tower placement will help make for an efficient alien-killing machine. Attempt to lock them into a dead end and they’ll just march right around your towers, taking the shortest routes and potentially circumventing your defenses altogether. You’ll have to erect your towers as a sort of fence, goading the aliens towards long, serpentine routes, to keep them in contact with your towers and delaying their advance to the power cores. Fortunately, an expanded arsenal and interesting mechanics will help turn the tide.Įach of your towers is surrounded by a force field, which the aliens dislike - it doesn’t hurt them, but they’d prefer to avoid it. A few levels later, and Defense Grid opens up entirely: you’ll suddenly find yourself herding angry alien sheep. The first few maps do a great job of easing you in: They’re simple, single path affairs, and there aren’t very many towers to choose from. Your final score is a tally of the remaining power cores, the value of the towers you’ve erected, and the total number of resources you’ve amassed. There are 20 maps in all, and to complete one, you have to survive all enemy waves with at least one power core still in your possession. But if another enemy intercepts that floater, they’ll scoop it up, and make a beeline for the exit. Kill them, and the power core they’re carrying will slowly float back to your power station. Once an alien reaches your power station, it grabs between one and three cores, depending on its strength, and hightails it towards the exit. The trick to Defense Grid is that the goal isn’t just to wipe out the enemy or survive each wave - you’re trying to prevent them from stealing your power cores.