The Indestructible UFO's are large, flying brain-like machines that only appear in the flying section of Mission 4 of Metal Slug 6. They are completely indestructible, as their name implies. While in the Slug Flyer don't get close to them because if you do, your Slug Flyer might get damaged.
- Contrary to their "indestructible" name, their meteor blasters can be destroyed.
- You can see them crash into the city in Mission 3.
- They are self-guided.
- The are more commonly referred to as "IVFO's" which stands for " Indestructible Venusian Flying Object".
|Human||Rebel Infantry | Arabian Infantry | Japanese Infantry | Pirates | Scientists | Ptolemaic Infantry | Natives | Hunters | Future Rebels|
|Undead||Mummies (Mummy Generator) | Dog Mummy | Mutated Soldiers | Zombies | Tar Man | Clones|
|Mutant||Bat | Chowmein-Conga | Ohumein-Conga | Enormous Moray | Jellyfish | Flying Killer | Man Eater | Huge Locust | Sasquatch | Maggot | Big Snail | Giant Caterpillar | Squid | Huge Ivy|
|Alien||Monoeye | Ring Laser Mecha | Hopper Mecha | Mars Mecha | Mars People | Big Eye | UFO | Mini-UFO | Invader Squad | Winged Invader | Flying Parasite | Hunter Walker | Hunter Lord | Scavenger | Crab-Tank | Vanguard | Smasher | Invader UFO | Indestructible UFO | Flying Core|