The best way I found to do it;

Ps. The colors on his chest mean;
Blue - Speed Attacks will not work on him (Amy, Espio, Shadow)
Red - Power Attacks will not work on him (Big, Vector, Omega)
Yellow - Flying Attacks will not work on him (Cream, Charmy, Rouge)

1. When you're Team Rose, use the first Team Blast right off to get invincibilaty, then switch to Big, and attack Metal Sonic. Right before you beat him, get the other Team Blast. DON'T USE IT!!!! Finish him off. Now, on to Team Chaotix
2. Used that saved Team Blast from Team Rose, right off. Then, swap to Espio, and turn invisable. Then, just throw kunai at him till his color changes to Yellow. Swap to Vector, and pound him till his color changes again. Swap to Espio again, and repeat. Make sure you get Team Blast!
3. As Team Dark, get all the Power Cores, then used the saved Team Blast. His colors change even more now. When his colors are Red and Blue, use Rouge. When his color is yellow, use Shadow. GET TEAM BLAST!!!!!
4. Team Super Sonic's is very hard. Used the saved Team Blast right off. Then, keep collecting rings. Metal Sonic will attack in 3 different ways;
1. Frontal Crystals- Use Sonic's Speed Dash on them
2. Geodome Spears- Use Tails to shoot SS & Knuckles
2. Throwing Eggman's fleet- Use Knuckles Super Punch
Just Keep using Team Blast! It takes 10 Team Blasts to beat him!