You earn interest on unspent resources. This creates a risk-reward dynamic where holding back on building towers early on can lead to a massive budget for late-game upgrades.

Unlike many tower defense games where enemies simply move from point A to B, Defense Grid utilizes a unique mechanic.

Some maps feature predetermined paths, while others are open grids where your tower placement determines the route aliens must take, allowing you to build elaborate kill-zone mazes.

Aliens enter the map, grab power cores from your base, and attempt to carry them back to the exit. If an alien is killed, the core slowly floats back to its housing—unless another alien picks it up along the way.

There are 10 tower types, each with two upgrade levels (Green, Amber, and Red strength levels). These range from basic Gun and Inferno towers to specialized Temporal (slowdown) and Meteor (long-range) towers. Performance & Features