After Shadow finds the third emerald, he gets willing to find more fast. So he travels to Prison Island to find the forth Chaos Emerald. Prison Island is actually a military base. There are three ways to get to this stage in story mode:
- Clearing the dark mission in Lethal Highway
- Clearing the normal mission in Glyphic Canyon
- Clearing the hero mission of Digital Circuit
In Prison Island it's your choice to either:
- Annihilate the GUN forces in the military for Black Doom (DARK)
- Find the White Chaos Emerald (NORMAL)
- Find the top secret disks that Charmy needs (HERO)
To clear this mission you have to destroy 40 of the GUN robots. Note that in Air Saucer riding sections, always take the lower routes and do not use the springs because some of the GUN robots are always there. Also, when your red gauge is full, use the invincibility you have gained to travel on the river without Air Saucers. Try to memorize the location of GUN robots to get an A Rank.
As usual, Clearing and getting A Rank for this mission is piece of cake. Just remember to use springs to get to the Goal Ring Faster.
You should find five top secret disks to clear this mission. Their locations are:
- A bit after when you meet Charmy, before the first spring.
- The first triangle jump section. Use triangle jump or the spring at the bottom to get to the other side, near the platform that has the disk on it.
- Use the springs in the Air Saucer riding sections to get to a path leading to the third disk.
- In the second triangle jump section (above the Goal Ring) ignore the Goal and use triangle jump to get above it. There's a disk above the Goal.
- Continue the path after the Goal Ring and the last Disk is at the end.
Scores for A Rank
- Dark Mission: 28000
- Normal Mission: 28000
- Hero Mission: 22000
- First Key: Jump over the spring after the first top secret disk and the key is in a wooden box.
- Second Key: In the first Air Saucer riding section, use the spring on the left to get to an area full of aliens that are protecting a cage. The key is in the cage.
- Third Key: After the third checkpoint, when you first face a giant worm in this stage, go to the left turn and look to your left. There's a small room and inside it, there's a wooden box containing a key.
- Fourth Key: Another Air Saucer riding section after the forth Checkpoint will bring you down a slope with a platform full of GUN robots on the side at the bottom. Go on the platform and move to the right to see a slab you can lift. Lift it and get the key under it.
- Last Key: After the sixth checkpoint, there's another Air Saucer riding section. Go down the slope and go on the rail on the platform at the end of the slope. Use double jump to get the last key.
The door is near the first spring after the third checkpoint and behind it there are two tank torrents which have wide explosion range.