Oh, what an interesting topic!
As many have already said, it is indeed a matter of design choice. Since we're talking about an existing franchise, then this design choice should probably follow this order of priority:
A) Does the game adhere to the pre-existing formula/ are you aiming to imitate the "official/authentic" type of game?
> If yes, silent protagonist is best. (Also, Red is officially not a silent protagonist hehe, see COPYCAT event) In case you wish to use the MC as a means to give out hints / direct the attention of the player somewhere, there are plenty of ways to do this outside of dialogue. There's the visual and the auditory approach. E.g., Link in LoZ:The Windwaker usually stares at nearby objects of interest whenever design dictates so. A strong sound or a faint one coming from a particular direction might also draw the player's attention. Emoticons/ sprite animation works too.
> If no, meaning our character can talk, consider the following:
B) Do you want your game to approach things in a conventional videogame way?
If yes, then:
1) Use the MC's perception to have the player notice things ("Seems like they're heading north")
2) Don't fall for the prolixity trap (e.g. repetitiveness of stated stuff, frequency of MC talking)
3) Avoid too much exposition ("so this is the famous so and so who does this and that")
4) Is the protagonist a predefined character with a predefined personality?
> If yes, then: You may have them comment in various ways, though you should still be careful in order for their writing not to feel forced.
The one who does the talking is the character.
> If no, then: The MC is still a reflection of the player, MCs remarks should be "neutral" and "colorless", eg:("It's a chair") not ("Don't tell me this piece of garbage is a chair, sheesh!"). This is not necessary if your character uses a "Mass Effect" dialogue option style where remarks are
categorized into particular responses.
The one who does the talking in this case needs to be the player.
5) MC talking should be a consistent feature, e.g. not disappearing (or appearing) when the player does not expect it.
6) Avoid passive voice and obscurity
7) Indirect remarks are still a great option for NPCs, even if the MC talks
8) Don't be breaking the 4th wall now.
9) No out of place/time/character remarks
10) Avoid letting your own approach to things/ views on a subject / take on a phenomenon slide into the MC's remarks.
11) No need for basic YES or NO, though that's not a bad choice per se.
12) Avoid exaggerated responses (of course in dire situations where something really bad happens, this could be different)
13) Avoid inner/outer monologue, except for cases where this is gameplay or "chapter" related. (e.g. a lot of stuff went down, devs have decided a recap should be shown)
14) It's a conventional game, not a book. Dialogue needs to be relatively simple, to the point, and laconic. Must not get in the way of gameplay and flow.
15) MC's choices are the Players' choices.
16) Be very careful - typos and, most of all, grammar, can make or break a game for some people.
If no, then:
1) Consider whether your main character is the narrator, if a narrator even exists
2) Naming the player can be used in....interesting ways (e.g. maybe you're actually naming a different family member, or it's a surname). Are you really naming the main character?
3) Don't let the main character expose everything, no matter how talkative they are.
4) Frequency, way of talking, idiomatic expressions, out of place remarks etc are relative to the idiosyncrasy, quirks and personality of the main character.
5) An annoying and logodiarrhea-ridden main character can be a deliberate design choice (in all other conventional cases, a No-No!)
6) The main character doesn't need to be a "link" to the player, nor a blank slate for the player to project themselves on.
7) Feel free to wrestle control away from the player, if they are starting to think that they're connected to the MC in a videogame "agency" way (e.g. disobedient to the player MC).
Does a predifined character have enough agency to break free from the player? How can this be exploited in a game design approach?
8) You do have to consider character development in an in-depth fashion.
9) The setting can be used to decide how you'll have your MC respond (e.g. is he in a foreign nation? Is the place there full of less-talkative people?)
10) Is your MC deliberately mute? By accident, from birth, etc. This is something that can be used in interesting design ways. Also, NPCs should remark on the MC's state.
11) If your protag is quiet by nature, you may use that as an opportunity to have him grow into a talker (and thus his talking will be a gameplay/story point of reference - and much more enjoyable to the player)
12) Make sure there's an indication of who's talking (visual, text, auditory. E.g. Name window, Mugshot, Emoticon/Arrow, JRPG low-budget voice-over "ahh" "hm" "I see" sounds)
13) Make the MC either relatable, annoying (yet bearable), flawed, and either ethical/non-ethical/mixed. Of course the latter might be "fluid" and not apparent at first.
14) Again, avoid letting your own approach to things/ views on a subject / take on a phenomenon slide into the MC's remarks - however, your MC will in all likelihood haev their own set of beliefs, opinions etc on something. Don't let your own personal opinions influence your MC or hinder you from creating a unique character.
15) MCs choices do not need to be the player's choices. A predefined character can make a choice of their own.
16) The MC can have a sort of inner/outer monologue even during inappropriate times or during particular events.
17) Put yourself in your character(s) shoes! That way you'll understand their..reasoning and you can tailor their responses/remarks appropriately!
Anyway, good examples of pokemon fangames which do the talking character thing well are: Super Pokemon Eevee Edition and Legends of the Arena.
