This gigantic unit was an ancient weapon that was discovered by Ptolemaic Army. Due to its gigantic size, it took them a large amount of time to excavate the weapon. Though it would have changed the war, the Ptolemaic Army was defeated before they could even be used in battle. The Stone Turtle could attack by squishing enemies with its massive feet and launching missiles from side launchers.
In Metal Slug Attack, the Ptolemaic Army managed to excavate the Stone Turtle after the war and would continue to develop it as such. A frog-like mecha was also discovered alongside the Stone Turtle, which was customized by Caroline and Towa. The mecha would then be used by Lucy. Another quadruped mecha was also developed by Caroline in reference to the Stone Turtle.
The Stone Turtle is an unused enemy vehicle. It may have been another mini-boss in the Final Mission of Metal Slug 5 as one of the unused areas, the end part of the playable flaming city section, is called "Turtle Boss", and its laser beam (more below) has background sprites from that level.
According to the game's sprites, the Stone Turtle has a built-in rocket launcher (similar to the Hi-Do) inside of its shell. It can lift their feet and move around the arena. The head is able to retract from its shell.
The underbelly opens up to reveal a laser beam. This beam has a sprite setup, similar to the tractor beams seen in cutscenes from Metal Slug 2/X and Metal Slug 3, where the background is also part of the laser sprite unlike the weapon laser beams which are opaque. This suggests the player characters would use the beam to go inside the Stone Turtle after defeating it and climb their way up to the Mammoth Tower.
It appears in game with a variant of colors.
The Stone Turtle appears as part of the 1.22.0 update, with a description explaining why the weapon didn't show up in Metal Slug 5. During development, this unit was named "The biggest unit" before being renaming it to the Stone Turtle in the release update.
The normal size has been reduced because the unit was too large for the screen. It mostly serves as a damage sponge, having 60,000 HP at level 40, slowly moving towards the enemy base and attacking by stomping on enemies. It uses the Hi-Do missiles inside its shell as its special attack.
It was introduced in Update 1.0.2. Just like in MSD, its normal size has been reduced as well due to its huge size. It has all the same attacks as well in its MSD counterpart.
- In the released official concept art of the Stone Turtle from Metal Slug Attack's pre-register event, the Stone Turtle was used as a base for the Gaia Elephant which can be seen in-game in the background at the very beginning of Mission 5. This references to the Hindu belief of a cosmic turtle carrying four elephants on its shell, which in turn carry the Earth on their heads.
- Its form resembles the AT-AT from Star Wars.
- The Stone Turtle's underside is reused from Dai-Manji
- The Emerald Turtle's color scheme is a reference to Raphael from Teenage Mutant Ninja Turtles.
- "Metal Slug 5 (Neo Geo)". The Cutting Room Floor. https://tcrf.net/Metal_Slug_5_(Neo_Geo)
- Gussprint. "Stone Turtle". The Spriters Resource. https://www.spriters-resource.com/neo_geo_ngcd/ms5/sheet/11439/