Runner

The runner is a fast robo that appears early on in the game. They appear to be robotic dogs that have yellow legs with a silver body.

While they have low health and armor, without slow towers, they can easily slip past your defenses since they are the fastest unit in the game.

You will receive $2 for killing a Runner. Later on in the game, they are a good source of income since, by then, your upgraded towers will be more than enough to kill Runners easily.