How do you add a character in a battle...

how do you add a character in a battle but then when the battle ends the character ain't in the party anymore. Like for a skill? (rmxp)

Add character to hero part
Enemy encounter
Remove character



EVENTS!

I mean like in a random battle. I made the skill so that in a battle you can add da player to your party and remove him at the end of the battle.

make a common event that adds the hero to the party, then the skill u use to call the hero has to call that event.  then u just need to fix it so that every time u leave the battle he leaves the party.