Sonic Generations

Can't Touch This - 30g
Took no damage from the final boss and cleared the stage.

What they mean by take no damage is that you can’t get hit by any of the Time Eaters attacks. These include the missiles, the swatting hand attack, the clapping hand attack, and the laser attack. The flying debris does not seem to matter when going for this achievement.

This was a very frustrating achievement for me. Be patient, this may take a few tries to get a good rhythm down. Here are some tips to help you out.

- If you don’t know already, you have to be in the right dimension to catch up to the boss and hit him. If he’s inside the stream then you must be inside as well (in the 3rd dimension), and if he’s outside the stream then you have to be outside of it too (in the 2nd dimension).
- In my opinion, it’s much easier to dodge and attack the boss in the 3rd dimension. If possible, try to stay there. If the boss is outside the stream you could risk switching to the 2nd dimension to try to catch up to him, or stay in the 3rd to focus on collecting rings. If you boost close enough to a line of rings they will be magnetized towards you.
- If you're having trouble collecting rings, my advice is to go slow and when you see a line of rings coming up, line yourself up with them and boost. This may be easier to do in the 2nd dimension, but it's not impossible in the 3rd.
- It seems getting hit by the debris will not matter when going for the achievement. From what I've read on the internet, people seem to be able to get this achievement even if they hit the debris, so it's just the missiles, the swatting hands, the clapping hands, and the laser you must avoid.
- If you’re about of be hit by a missile, there are two things you can do to save yourself. You can shoot the other Super Sonic forward with the "A" button to destroy the objects, or you can press the "Y" button to switch to the other dimension and essentially be shot away from any danger. It will be harder to catch up to the boss if you choose the latter method, but I personally liked using the "Y" button to avoid danger. You cannot switch dimensions if the other Super Sonic is not with you!
- The swatting hand attack is easily avoidable. Keep boosting and fly away from the hand. Only a few times was I ever hit by this thing. It's mainly the missiles and clapping hand attack that you'll have to worry about.
- When you fly in for attack, the Time Eater will usually try to clap at you. To avoid this attack, I found going up and above the bosses face is easier, even if his upper hands are trying to smash at you. After he claps, fly down towards the target and keep holding the boost button, and you'll get an attack in.
- To avoid the laser, simply switching dimensions is usually enough to dodge this attack.
- There is no time limit for this achievement. Take your time and avoid danger most importantly!

Below is a video for how to get this achievement. Full credit for the video goes to Vandelay16 of Youtube, and thanks to Professor Pie for pointing it out to me.

There are a couple of tricks / things to be aware of:

- You need to position Sonic so that he is directly between the core and the camera (so graphically he is covering it) for him to catch up to the Time Eater - I've not seen this noted in any other guide.
- Use 3d mode almost all of the time, switch only when you need to to avoid the laser, hands or homing missiles (normally you can just dodge the hands and missiles though).
- Don't ever press A as it stops you switching dimension - debris doesn't count on this achievement and you can easily dodge it anyway.
- Sometimes Sonic gets"stuck" on the upper or lower "walls", usually when dimension switching while the "level" is sloping up or down. Switching back and forth should push him back into the middle.
- You can move much more when NOT boosting so if you need rings, slow down before boosting through them.
- You can avoid the crush move and not lose too much ground by hovering around his face. Sometimes you get lucky and it gives you an easy hit at the core too.
- And the best one last - turn off the annoying voices by reducing the sound effect level to 0 in the options.

First of all, this is NOT impossible. You're just gonna need a lot of patience.
I've been able to settle some things down as I tried (and eventually obtained) it:
- His "physical" (punches, clapping, etc.) attacks DO COUNT. Make sure you're not hit by any of those.
- Everything else (missiles, level debris, etc.) also counts.
- Make sure you have audio and rumble on. I know it can be annoying, but they are excellent tellers for whether you were hit or not.

For general tips on the boss/how to avoid attacks, follow the video posted by Sonic Cyanide: