Metallic Madness is the final zone of Sonic CD, and is fittingly the penultimate zone here (not including the Sonic-exclusive Egg Reverie). Using catapults and rotating platforms, you are able to travel between the background and foreground of the zone, and if no other path is available, shrink rays drastically change the characters' sizes. The achievement/trophy for this zone can be obtained during the second act's boss, and is easiest accomplished with Tails (as he can stay in the air).
Act 1[edit]
Jump over the spikes and onto the next platform, avoiding the saw-carrying Mecha-Bu in your path. At the end of the platform is a list that will put you in reach of some small flipping platforms. Hop onto the spring to reach higher ground (if playing Sonic, a Spin Dash and a jump will help you reach the Shield behind the spring from here). Continuing forward, use a spring to reach higher ground, avoiding the following springs that attempt to send you backward. When you run into the Matryoshka Bom, simply hide behind the short wall it stands on until it explodes, as you won't be able to do damage to it. Continue to jump over gaps and springs, maintaining your high ground, to reach the first Star Post. Drop down into the subsequent gap to run into your first catapult, which will launch you into the background. Find the next catapult here to return to the foreground.
After passing the second Star Post, drop into the next gap and upon being launched upward, veer left to find a Lightning Shield. The spring on the other side leads to higher ground, where you can find another catapult to take you into the background. After returning to the foreground, you should find the third Star Post. Hop along flipping platforms and across some more gaps to reach a rolling spring. Time your jump through the gap to come across another catapult. After escaping back to the foreground, you'll end up another catapult that will launch you right back into the background. Spin Dash through a barrier and use the catapult at the end of the path to reach the final Star Post. Past this is the first act's boss.
To deal some damage to Dr. Eggman, watch for which pistons are shaking (either from the ground or ceiling) and try to get between them (but be cautious to avoid being crushed). Hit the piston holding Eggman, then watch for the next set (after avoiding some projectiles). After four hits, the pistons will speed up. Simply keep moving to avoid getting crushed and watch for Eggman. Another four hits is all it takes for him to retreat.
Act 2[edit]
Drop down from some crumbling ground twice to find a Super Ring Item Box. Avoid getting crushed by the pistons and drop down the gap at the end of the path. Walk into a red laser to shrink; this will allow you to proceed forward in places you normally wouldn't be able to fit into. Walking into a blue laser will return you to your regular size. Across some circular platforms is the first Star Post. Proceed past the spring, into another shrink laser. Climb some more circular platforms, then drop down the narrow tube to the right. Drop further down to set yourself on the path to the next Star Post and a growth laser. Past the wall is a unique area.
Some purple lasers at the top of the screen will be your only indication that some spikes will come crashing down on you. Take note of the gap between the spikes and position yourself directly under that gap, causing the spikes to simply crash down on either side of you. Use these spikes as a step upward, then watch again for the next set of spikes. Continue this pattern until you can reach the spring to the left. After escaping that area, use a spring to avoid the first gap and drop into the second. Continue to the right and step on the rotating platform to find yourself in the background. The next rotating platform leads back to the foreground. Proceed forward into a shrink laser, then follow whichever path you prefer to the boss.
The Gachapandora is fought in a miniature state, and fittingly enough, Eggman will send his toys after you before giving you the opportunity to deal damage to him directly. Turn the knob to release an enemy (either a flying Eggman, a driving Eggman, or an explosive robotic Amy which can be taken down with a Spin Dash) and defeat them all before turning the knob one last time to release the real Eggman, giving him no choice but to retreat. For the achievement/trophy of this zone, you must release all eight enemies without destroying any of them (keep in mind that the miniature versions of Eggman take three hits each to defeat). As was mentioned earlier, Tails is best for the task, as he can stay in the air, out of reach of all miniature enemies, and simply pass by the knob as he flies to turn it.
After Eggman retreats, you can proceed forward to find a laser that will return you to regular size and as always, a capsule full of imprisoned animals. You can now move on to the final zone.