Based on tortoises, Gustav Turtles are large Badniks with a heavy turtle shell and a huge grey cannon on their back. On their head, they have pink cheeks and tired-looking eyes. They also walk on four legs and have a small tail on their rear.
In the Wii U version of Sonic Lost World, a single Gustav Turtle appears on a small planetoid in Sky RoadZone 1. Surrounding this planetoid are two looping Clouds, the lowest of which the player lands on. When spotting the player, the Gustav Turtle starts firing missiles into the sky, which then drop down and get stuck on the upper cloud ring for a couple of seconds before exploding into flaming lines. Before one of the missiles explodes, the player must use the Cloud to bounce Sonic into it, causing the missile to fly back at the Gustav Turtle. Hit the Gustav Turtle a total of three times to defeat it and make the Planetoid Spring appear on the Cloud ring.
In the Nintendo 3DS version of the game, Gustav Turtles are more common and are found in Silent Forest Zone 1 and 2. Here, they appear on their own alongside smaller Badniks. In gameplay, they remain stationary until the player's arrival, upon where they start moving towards Sonic slowly while firing cannonballs at him. Gustav Turtles are some of the tougher enemies in the game, but it is sometimes mandatory to defeat them to open Cases, which are needed to proceed within the Zones.
In battle on the Nintendo 3DS, the player has to target the Gustav Turtles' heads. Use either the Homing Attack or Somersault Kick to stun them for a few seconds and then use a fully charged Focused Homing Attack on them. After this, the Gustav Turtles will hide their heads inside their shells for a few seconds before creating a short-ranged shockwave with a short jump. Use this strategy three times in order to defeat the Gustav Turtle. Alternatively, the Gustav Turtles can be taken down with two hits from the Gray Quake and only one hit from the Ivory Lightning.
Like many new enemies in Sonic Lost World, the Gustav Turtles' name has not been listed in any official source. Instead, it is referred to as "gustav turtle" in the game's source code.