what should I make to catch the third emblem of the last stage of the game?

Mission 3 completion?

First of all, go to the SA2B forum and read the walkthrough for a 6-second time on mission 1.

You don't need to understand all of it--just the part that deals with permanently stopping time.

Anyway, play through Tails, Eggman, Rouge, and Knuckles in the normal way. (There are Mystic Shrines in the latter three stages--but believe it or not, you DON'T HAVE TO USE THEM!)

Once you get to Sonic, you can choose to go for the permanent time stop at either the first switch or the second switch. Unless you're running dangerously close to the 7:30 A rank time limit, it doesn't matter which switch you use (and the second one is a good deal safer).

You have to get the time stopped in order to make the next section work. Now, proceed to somersault under the barrier and jump to the tunnel. Upon emerging, make it to the top of the hill, and STOP.

Walk backwards, onto the "wrong" side of the hill, a short way. You're going to attempt to spin dash up, and at the very moment you reach the top, JUMP as high as you can. Be sure to hold Up on the control stick so that you gain distance as well.

At the very top of your jump, tap A again. If you jumped high enough, you should barely make it onto a ledge. (If you didn't make it, don't worry--just run backwards to the other side of the hill, and try again.)

Now that you're on the ledge, you can strike the two enemies with impunity. Doing so opens the door, behind which you can find the Chao! Tag it to end the level.

The world record with this strategy is 2:14.37.

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