SONIC THE HEDGEHOG

Get an S Rank on End of the World and the Solaris Battle.

The Solaris battle isn't all that bad, in the first phase of the battle just alternate attacks between Silver and Shadow whenever he starts deflecting you attacks, when the armor on his arms are broken off he'll hold his arms out and that's the signal to switch to Sonic, just keep attacking his core (don't forget to charge your attacks with right trigger) and the first phase is over. The second phase I believe anyone is able to attack now, just switch characters whenever he starts deflecting, before you know it you're done. I S ranked the first time and I barely knew what I was doing so I'm sure you'll do fine on this one.

The ACT level (End of the World) is the one to worry about, if you thought the game sucked up until this moment, then man will you need the patience of a saint to pull off an S Rank here...

My basic advice is to memorize routes that work best and help shave seconds off the clock, your point score will help indefinitely in the end, so keep in mind dying any time after Tails or Omega should be unacceptable, rings will help your score (they're worth 10 points a piece including individual rings in item boxes) in the end but don't worry too much if you lose some before you get to the last level, and hope to whatever deity you prefer you don't get hit by an exploding box when you're next to a gravity well. Practice certainly makes perfect here.

If you want a more in depth guide check this walk-through out:
http://www.gamefaqs.com/console/xbox360/file/929717/45811
But if you feel comfortable in you abilities and memory of the game go on ahead.

Here's a basic time sheet of what I was able to pull off, stay within these time lines and you should do good.

Tails: 0'50"
Omega: 1'00"
Knuckles: 0'30"
Silver: 1'55"
Rouge: 0'40"
Amy: 1'30"
Shadow: 1'35"

And now a brief character guide-

Tails: Fly don't run, spam Tails' aerial attack on anything in your path (boxes included), just don't go out of your way for anything, always keep a forward momentum. You may grab some item boxes but only if they are directly in your path. The emerald is on the sky scraper furthest back to the right.
Omega: You may make use of your homing attack here but by no means you should let it slow you down, you should also make use of Omega's jumping height and hover ability, there's a technique that stretches his hover distance called 'peppering', by tapping the jump/hover button Omega will lose less air time and will hover further, be warned though as I read the PAL version of peppering might be different. Just avoid gravity wells and you should do fine. You'll find the emerald as you go along the level.
Knuckles: Don't waste any time as Knuckles, just make use of his glide/wall climb ability, memorize the best route, and make it to the emerald as fast as possible. The emerald near the end of the level on a large square platform.
Silver: Don't worry about the enemies here too much, like always make use of each character's special ability, there's a patch of five worm things you can take out here, doesn't matter if you kill them skillfully or not, if you activate the eagle statue before getting to them then you'll need the couple seconds of delay killing them, if you hit the statue and attempt to go on as fast as possible you may come along a path with spiked balls and gravity wells that are positioned too close to eachother, this may well be a trap and will cost you your run when it works. Again you'll find the emerald at the end of the level.
Rouge: Make use of the abnormally tall mountains here, use the first two shorts one as your starting point then fly to the closest tallest one and jump off the top of it and make your way to the beach, the emerald will be right on the shore.
Amy: You know you've experienced hell when you play as Amy when it's the end of the world, seriously this will be your hardest run of the the act. Memorize a path, don't stop for any enemies besides the two guarding the door near the end, if you wish memorize and utilize her awkward invisibility (hold X), be careful though as she stops dead in her tracks whenever she activates it and when it wears off, which sucks because that happened to me when I was trying to get past a gravity well so be warned, this run will take a lot of patience on your part, try not to get too frustrated.
Shadow: Okay, you've come this far don't do anything you think might be risky enough to lose a life over, just find a good path and go with it, there's a few notable thing that can help you here though, at all costs use the rainbow(/boost thing) ring, it can save you time and from using a very dangerous path, a light dash line of rings leading to a 1up box (worth 200 points), and a small floating island with three item boxes next to the emerald containing two 20 ring boxes and a 1up. Exercise extreme caution here.

The score to rank guideline is:

Rank - Score
S - 50,000
A - 45,000
B - 25,000
C - 5,000
D - 0


My score for getting the S Rank was:
Time: 7'56"
Score: ~15,000
Rings: 76

So as long as you get under eight minutes and have a good score you can get away with having a low ring score. So obviously the ratio between score prior to winning and ring amount can obviously be used to your advantage here. Preferences may vary so good luck!

Here's some general tips for each character:

Tails:
-Walking is way too slow. Fly instead.
-While flying, drop bombs on enemies that are in your path, but don't bother going out of your way for every enemy. Just make your way to the Chaos Emerald.

Omega:
-Jumping and Mashing X for an attack is your best bet for killing enemies.
-Be sure to abuse the glitch that allows you to glide past huge chunks of the level.

Knuckles:
-Glide, don't walk.
-Don't bother going out of your way for much, except maybe the eagle statue that's directly on the path to the Chaos Emerald.

Silver:
-This is where you need to start trying for the S Rank the most.
-If you die as Silver, then it's no problem. Any points you've earned can be made up by killing most of the enemies in Silver's stage.
-Use the glitch that lets you fly farther than normal to get across any bottomless pits.
-Take this portion of the End of the World a bit slow. Silver's level seems to have the cheapest placement of black holes and holes that shoot boxes at you.

Rouge:
-Climb to the tops of the really large rocks, and glide to the Emerald from there.
-Like Knuckles, don't bother going out of your way to get anything.

Amy:
-You'll want to get through this as fast as you can, but at the same time, you might want to take it a bit slow at times to avoid the black holes.
-Don't attack any enemies except for the two at the end needed to open the door to the Emerald.
-Don't waste time using the invisibility power, it's better to just run past everything.

Shadow:
-Kill plenty of enemies for plenty of points.
-Collect as many rings as you can and avoid getting hit.
-Use routes that involve going over a bottomless pit at your own risk. Chances are, you will mess up on them at least once in all of the times you may be playing this to get the S-Rank.
-Use the Rainbow Rings to jump past portions of the level and get points from them as well.

This is how I did it, and after maybe four or five tries, I got it right.