Maybe this has been suggested before, but I have an idea for multiple characters in a party.
As follows:
When you are walking around you can press hotkeys to select which player you wish to be. (As long as you didn't have a party made of Darlene Dasha and Diamond, or Tim Tom and Tabernacus.)
When you change to another character, your stats and abilities also change.
You also fight as whoever you are (unless you have turn-based combat.).
As far as dialogue and plot goes, you could have a global that marked what character you currently were, and several conditional globals for which characters are in your party.
Can you please point out any faults that you see in this idea.
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Poor little Johnny, of whom we'll see no more, for what he thought was H2O was H2SO4.