BATTLE PARTY SIZE AND BALANCING

I like MMO-style parties with distinctive roles so a 5-man party works best for me. I don't start the player right away with 5 members though so the battle gameplay gets gradually more complex as the game goes on.

Here are some common setups for parties:

One character per role
- Maybe you need a tank, healer, magic damage dealer, and physical damage dealer. Or maybe you need a stunner, healer, single-target damage dealer, and AOE damage dealer. Or maybe you just need a damager+healer and a damager+stealer. Depends on the game!
- The key here is there's a 1:1 ratio. If there are three roles, there are three characters in the party.
- Maybe you hard-code it so the player is forced to bring one character of each role, or maybe you just make it so the party stands no chance otherwise.
- You probably want the player to get a full party very early in the game.

Everyone is a jack of all trades
- Party size in this can technically be as large or small as you want.
- Larger parties will feel rather pointless, since additional characters don't bring much to the table.
- This is probably the style of party that's gonna be used by most games where your max party size changes in different dungeons. Dropping temporarily from four characters down to two changes how you play, but you can still play with just two characters without any problems, or even with just one character.
- Similarly, it doesn't matter how long it takes to get a full party. Maybe you don't get it until near the end of the game! If you go most of the game without a full party this is probably the style you're using.
- Since everyone can heal, the bigger the party is, the easier healing becomes. You can spend a single round making everyone focus on healing or on defense or whatever, so past about three characters, it becomes increasingly difficult to make the enemies threatening without letting them one-shot a character. Especially if your game has any AOE heals at all. In a CTB or ATB system where you get turns in between the enemies, this is less of a problem.
- For example, if you have five characters, an enemy can kill two characters every turn and still not be any kind of threat at all. Because no matter who dies, the remaining party still has two revivers and one damage dealer.

There are a bunch of roles, and each character performs a few of them
- This is the style I personally prefer in games where you can choose who is in your party (or in games where you can customize the roles and skills of your party), since it turns party-building into a puzzle that keeps me interested.
- Maybe one character inflicts ailments, grants haste status, deals decent damage to normal enemies, and uses an AOE heal. Another character deals good damage to bosses, bad damage to normal enemies, takes advantage of elemental weaknesses, and recovers the party's MP. Another character inflicts debuffs that are good against bosses, improves the party's defense, deals decent damage to all types of enemies, and pierces defense of otherwise very hard to kill rock-type enemies. Etc.
- There'll be a lot of overlap between characters, especially since you probably don't strictly need every single role to be covered. But each character still will feel unique, and the player will care a lot about the party size because they can do so much more with more characters.
- The number of party members you allow the player to use will depend on how many roles you have, and how many roles you give to each character.
- Some of the roles (like dealing damage and healing) are things the player will want to have more than one of, but others (like casting a specific buff) are things that have no benefit if you already have someone who can do them. This naturally creates a maximum size you should allow. If the player has enough party members that he's doubling up on roles other than damage and maybe healing, you have allowed too many characters to join the party!
- This is the type of game where temporarily giving the player a different party size than usual can work, but will drastically change how the game is played.
- Dropping the player temporarily down to just one character will probably make the game nearly unplayable, except maybe during a tutorial dungeon where you learn to use the character.

Design the power of multi-target skills vs single-target skills and the frequency of death spells and disabling effects according to party size, not the other way around.

As for the party size, 3 to 4 is usually the best number, but that's not a given.

You want may to consider the total number of available characters. I find it rather annoying when a game has a very large pool of characters compared to party size. That makes rotating them to bothersome, while permanently benching someone makes me feel like the character isn't really contributing. This can cause a problem if a cutscene then contradicts that idea. I also find it weird if you have one more character than the party size for an extended amount of time.

How the characters' skills are set up also affects what's a good party size. As a rule of thumb, the more flexible they are, the less you should allow. It's hard to say exactly how many should be allowed, but you can ask yourself how wide variety of actions the player can cover with a certain amount of party members. If the players can get everything they can possible want and still make everyone a good damage dealer as well as getting more healing than needed, the player has too many party members. However, if the players struggles to merely get the bare essentials, they either need a larger party or more flexible characters.

1) If your turn style is "characters take turns based on their agility, and everyone chooses their action when it's their turn" then you have a lot more leeway on how many characters to put on the team. The player can respond to each enemy action - the character who goes after that enemy just has to be able to respond to it. If the player has 10 party members, and only #2 and #4 can respond to the enemy action that just happened, it's going to be a problem. In that case you need fewer party members, or the party members need to each be able to do a wider variety of things. This is why I made my post above about roles of party members.

2) If your turn style is "characters take turns based on their agility, but you input all of their actions at once at the beginning of the round" then 4 is probably the max, and I'd personally go with 3 from my experience. The more characters you have, the more enemies you'll need to have, and thus the more enemy actions you'll need to predict instead of just responding to. It gets ridiculous when you're making your third and fourth characters use heal spells on people who are at full health, because you're worried that 2-3 enemies might attack them before the heal spell goes off.

3) If your turn style is "your party acts, then the enemy party acts" then the player's goal is going to be to take out enemies before they get a turn. You probably want to give them enough characters to actually accomplish that! 3 won't be enough probably, at least not enough to make it interesting (which you're probably doing by making the characters better against certain enemies). 4 might still not be enough if they need buffs before they can start attacking.

The upper limit on this third turn style is that the party has to be small enough that if you do a bad job on the first round, you can't have so many party members that the enemies still don't stand a chance. If you accidentally leave 1-2 enemies alive, but you have 12 characters, you're still pretty much invincible. Tactical RPGs can get away with it though because they use positioning to make new enemies join the battle each round - a traditional RPG could probably do the same thing just by literally having new enemies join the battle each round. Might be interesting, giving the player a dozen party members but having more enemies spawn as the battle continues. On the other hand, if you're not trying to let the player pick off most of the enemies before they get a chance to act, then... why are you doing your turns this way?