Is there a strategy to beat the final boss?

Kinda. When the circle object that is on his body is blue, you can't attack with the speed character, when it's yellow, you can't attack with the fly character and when it is red, you can't attack with the power character.

The best way to beat him is to use fly and power formations and when you get team blast, use it!

As for using Team Sonic when Sonic goes super, keep collecting rings and boosting around until you get team blast.

Keep doing this throughout the battle.

To beat Metal Overlord, you have to use team blast at least 4 or 5 times, I can't remember, but I know it's more than 3 times. Anyways, in order to do this, it is plain to see you have to charge your team blast meter, and you'd have to charge it fast. To do this, it is important to remember Metal Overlords three key attacks (not including his paralyzing bubble attack). His first type of attack is his freezing Ice ball attack, when he uses this switch Super Sonic to leader and have him use his sliding attack to break all of Metal Overlord's iceballs. His second attack is his spine attack, in which he shoots missiles out of his back that will cause you to lose control of your character for a bit (don't worry, the character will regain his footing in a couple of seconds). For the spine attack, it is recommended to use tails' thunder shoot to blast the missiles one after another, it is also a good idea to have sonic use his light attack, which can be activated after jumping in the air while nearing a missile, and pressing the B button when you see the flashing red B button located right of sonic's speed symbol. His last attack is when he dives under the sky and picks up one of Eggman's battleships, in an attempt to knock you out of the sky, when this happens, switch to knuckles as leader and have him do his three in a row attack in which after three punches are thrown, he slams his fist in to the ground and fire balls are launched everywhere; of course, in super form, when knuckles does this, he is able to continually throw fireballs as long as you continue to rapidly press the B button, and you can also control where you are throwing the fireballs as well. All of these matchups are designed to quickly charge up your team blast meter, and make sure to keep your rings up, since Metal Overlord can also use Chaos control, which if your ring count is low enough, will force you out of super mode because it can potentially run you right out of rings. Good luck!!

Kinda keep pressing y+b at the same time in fly formatoin on any team (this gives you a teamblast meter boost, a big one.) and keep using team blast. (i don't think team sonics team blast special ability works on this guy.)

The colour of the circle is the character you can't fight it with.
With Chaotix you need to have level 2 characters and Dark level 3.
As for Metal Overlord, fill your team blast guage and use it on him 3 times.