The Protogunner does not have any kind of protection for the operator but is invincible. Unlike the final product, the Protogunner cannot transform, and it lacks the Gatling gun and pile bunker. However, it still retains its 180mm multiple cannon on its front along with a pair of 10mm Vulcan cannons on its side.
The Protogunner is much lighter and maneuverable than the Slug Gunner. Although it does not have the jet pack that allowed the Slug Gunner to double jump, the Protogunner still jumps reasonably high even without it.
By holding down the fire button, the Vulcan cannons will be fixed. This makes the Vulcans lock in place and allows the player to move the Protogunner and continuously fire without moving the Vulcans themselves.
In Other Games
The Protogunner is a relatively fast-producing heavy walker capable of long range fire support. It has an average amount of HP comparable to the finalized Slug Gunner with decent armor and damage. The height of its jump special allows it to very easily land hits on passing air units including R-Shobu, although it doesn't deal enough damage in one shot to destroy one. When destroyed, Ralf jumps out before it explodes and fights on foot; it is unknown on how upgraded this Ralf is.
The Protogunner returns with the driver changed from Ralf to Tarma due to the former's Super Rare, pre-acquisition status and originally being a powerful unit. New variants are introduced, although the drivers aren't playable when the Protogunner is destroyed.
Metal Slug Attack also introduces the Slug Defender, a heavily modified Protogunner that attacks with electricity.
- Protogunner: The original Slug Gunner prototype.
- Protogunner Type-B: A blue-painted, upgraded model of the Protogunner introduced in Metal Slug Attack.
- Golden Protogunner: A golden-painted variant designed for mobility and able to evade by jumping. Once its HP is gone, Fio pushes it towards enemy lines before escaping.
- The Protogunner has unused animations of firing at recoil while jumping. The animation gets used in Metal Slug Attack as the Golden Protogunner's special.