The battle system in Mother isn't hard to understand, but here are some hints that could help you on this journey.
Before the Battle
The only way to level up in Mother is by battling enemies. For each enemy you defeat, all your party members receive a set amount of experience points. As the game progresses, the enemies get tougher, so don't fret if you die a couple of times.
The encounters in Mother are entirely random, so you'll just have to be prepared. Because the encounter rate is so high, it's easier to run away. Remember that.
Use the Check Function! (Mother only!)
In the Japanese version of the game, using the check function could be your trump card. If you use "Check" and get a message that says "もんだいなし。" (mondai nashi, "There's no problem."), then the area's safe; but a message that says "あやしげなけはいが・・・・・・。" (ayashige nake hai ga, "It feels suspicious."), then expect a battle to take place! It can be pretty helpful to know where battles are going to take place, so why was this removed from the English version?
Just like outside the field, there are numerous commands you can perform inside the battle:
- Fight - Attack the enemy. If there are multiple enemies, you are allowed to choose. If the enemy you choose is defeated by someone else before you go, you will not attack anything.
- PSI - Opens up the PSI Menu. You can then cycle through the PSI options (assuming you know PSI) and choose a PSI attack to perform (if you have enough PP).
- Goods - Opens up the Goods Menu where you can select items.
- Check - Allows you to check the enemy's weaknesses.
- Auto - Put the game on Auto Fight, where the game fights for you. This affects all members of your party.
- Guard - Increases defense for one turn.
- Run - The entire party tries to run away from the battle.