I think lasers could be a good addition, like a block with a barrel that shoots a laser. Depending on whether the block is fixed or not, you can push or rotate it by walking along the side of the block.
There could also be a receiver for this laser that, upon receiving the laser, would disable energy shields and make certain things killable. Mirrors would be nice as well.
(The laser itself doesn't kill any units; the unit will block the laser from passing through it.)