Sonic CD
12 Achievements
200
8-10h
Treasure Hunter
Collect all the Time Stones
20
How to unlock the Treasure Hunter achievement in Sonic CD - Definitive Guide
The stages themselves are unique to other sonic games, the goal is to knock down spaceships in a 3d plane. The first 4 stages are very easy, the last 3 however are pretty difficult and will possibly take multiple tries.
I found that though you can't save when you want like previous Sega arcade titles, you can quit in the middle of a special stage and return from the menu, it won't take you back to the stage before the stage, but it will take you back to the special stage itself! Exploit this to your hearts content. You should have all the time stones by Wacky Workbench 1 or 2
Edit: If you run out of time in a special stage, you will be taken to the next stage and will not be able to return to your special stage save. So if you have less than 10 seconds or 20 seconds when you're above water, pause and go back to the main menu so you don't lose your progress.
Credit to SangMaitre for the videos
To collect a Time Stone, you will need to finish a Special Stage. In order to get to a Special Stage, you will need to finish any Zone 1 or Zone 2 with at least 50 coins. Once you see the sign with Dr. Eggman giving a thumbs down on it, you should see a giant floating coin behind it. Jump through that coin. It will take you to a Special Stage.
I would highly recommend backing out of the game at this point in time, and copying your file to a memory stick or any other storage device. It is very, very easy to run out of time on the Special Stages, and when you do, the game saves automatically and pushes you to the next stage. If you copy your file to another storage device, at this point you can just back out of the game, recopy your copied save to the storage device that you play the game on, and play the Special Stage over again.
Once you start the Special Stage, you will notice there are a lot of flying UFOs. You will need to jump into all of the flying UFOs in order to destroy them and finish the stage. If your timer falls below twenty seconds, you will notice a new UFO in the middle of the stage with red lights. Go over to that UFO and destroy it to have your timer bumped up by 30 seconds. The timer UFO respawns every time your timer falls below 20 seconds, so you can continuously bump up your timer until you finish the level. You can get Time Stones on any Zone 1 or Zone 2 levels. There are 14 possible chances to get the 7 Time Stones, so don't fret if you miss a chance to get a Time Stone or two.
To get to the Special Stages in Sonic CD you have to get 50 rings and make it to the end of the level and jump into the giant ring at the end. Once there, you have to destroy all UFOs in the level before time runs out. Touching the water will make time drop drastically and when time gets low a new (blue) UFO will appear. It will make a sound when it appears and will stay in the middle of the level. When this UFO appears you need to destroy it to get more time. Destroying all the UFOs in the Special Stage will award you with a Time Stone. There are seven Time Stones in all and they can be gotten in all first and second acts in the game. In this version of the game the UFOs are properly scaled so you will be able to judge your jumps better than in the other versions of the game. This achievement will pop during the Special Stage score tally after you have gotten your seventh Time Stone. NOTE: If you do not get all 7 Time Stones in one playthrough you will have to start another playthrough and try again.
If you are having trouble in a Special Stage (like time running out and there is nothing you can do) just exit to the main menu from the Special Stage. Your save file will be on the same special stage when you get back to it so you can start it over.
Here is a video of the special stages in the game:
Sonic CD - Special Stage run - YouTube