First you must beat the Subspace Emissary mode. Then you must go back to the Forest stage. In this stage you will find the door to fight him (it is near the beginning of the level). Beat him to unlock him.
you mean pikachu yes
It's not. You can only face them in the Subspace Emissary or Boss Battles.
Finish the subspace emissary.
Beat the subspace emissary.
You . . . don't. There are only two ways to unlock characters in Brawl: either have them join you in The Subspace Emissary--and there are multiple ways to do this, depending on the character--or fulfill the requirements outside of the Subspace Emissary, like completing Classic mode in a certain time limit, and best the character in a one-one brawl. That's it. If you don't want to go through the Subspace Emissary to unlock characters, you'll have to brawl with them. If you don't want to brawl, go through the Subspace Emissary. There is no third option.
You can play as him in the Research facility levels, and the Subspace Bomb factory levels.
Beat Subspace Emissary then he appears
Having him join you in subspace emissary is the easiest and fastest way.
it is in stadium in solo to unlock beat the subspace emissary
Unlock him through the subspace emissary.
complete the subspace emissary you should now be able to play him.
Finish the subspace emissary mode.