Well, if you are Tepig or your partner is you have a big advantage but if not:
"When you enter the mode, you have the ability to select two Backup Pokémon. Similar to how they'd come in a pinch during normal battles, these Pokémon will come in and attack the enemy, doing damage while they go. This is very useful in order to try and cover any type disadvantages brought on by the other Pokémon you face. To activate them, all you have to do is press the A Button at any time. This calls them into battle and they shall quickly attack, do the damage, and then leave. You can only use each backup Pokémon once per round, and you cannot skip one to get to the other one."
I hope this prove's successful for you :)