All the original characters in Sonic Adventure have add-ons they have to get to beat the game 100% and to get all 130 Emblems. They also have other PowerUps you dont have to get but make things easier. Those are the following:

Sonic:Speed Bracelet:Go above the front desk of the hotel in Station Square.Start charging up your attack. If you stand in the right place the doors will open. Go inside to get the bracelet.

Tails:Jet Anklet:To obtain Tails's Jet Anklet, simply go in the Staion Square sewer near Twinkle Park and fly up the hole in the roof to find it in a little room.The Anklet makes Tails fly longer and higher.

Knuckles:Maximum Heat Knuckles:To get the golden Heat Knuckles (which lets Knuckles perform the Maximum Heat Knuckles Attack), go to Big's house in the MR. Youll see a ledge above. Go up there and *BINGO*. Youve got your PowerUp.

Amy:Long Hammer:For Amy's Long Hammer,you must first have her Warrior Feather. Then just beat 2000 points on Hedgehog Hammeragain and theyll give it to you.

Big:Good Rod:You probably saw the green light under Bigs bed in his opening movie. Once your in the game just go back to his house and lift up his bed by pressing X or Y.

E-102:Tri Gun:E-102 has an updated gun, which you get after the Water Resevoir in the core of the Egg Carrier is enterable and the water is drained. Its just sitting there.