How do you hit a rival with a power up in sonic rivals?

When selecting character press Triangle

You can't be him in that game.

The mystery character in Sonic Rivals is Metal Sonic. To win him, you have to beat the game once with every character. Doesn't matter which order. You can also win Super Sonic. but that is Xtremely...

Usually to be Super Sonic, you have to get all of the Chaos Emeralds. If you can gather those, you will either beat the game or unlock Super Sonic for play.

You have to unloock diferrent Cups and play Multiplayer to unlock character costumes