LOL!
Ok, let's get to work.
Multiple Damages - SephirothSpawn (Nice addition if you really want it. But I remember a script that messed up the actual damage numbers, IDK if his does. Can be added anytime (or removed if it starts annoying you).)
Stat Bonus Base - SephirothSpawn (Wouldn't that be easier to make with event...? -_- I'd say screw it, you won't need it most probably anyway)
Actor Stat Bonuses - SephirothSpawn (Well, can be a bit of useful sometimes. But when I think of how many critical script parts need to be modified, I have the right to doubt that it is even compatible with SDK itself. xD I don't think anybody uses that. At least I wouldn't. Add it from the beginning to avoid inconsistency)
Character Sprite Frame Change - SephirothSpawn (WOW! This can be done by changing one number in the scripts. I know, I did it in my game, too
without having a script that is probably over 100 lines. Anyway, delete it right away after you saw what it changes, find that line in the default script and change it. EXCEPT of course if Seph completely overcomplicated it. Do what I said anyway, I'll tell you which line it is if you need it.)
Class Support - SephirothSpawn (So like, the more people have the same class, the higher their stats increase? COULD come in handy with a party changer where you actually have control over something like that. I'd say add it right away or leave it. It can cause inconsistency if you add it later.)
Damage Reductions - SephirothSpawn (I actually think that an unreadable docu is a compliment for Seph. -_- And yes, the database can do that. At least add stats, it can't "multiply" the value, but who would want that?! You should decide whether using it or not right away. It could mess up the consistency in your game pretty hard if you add it later.)
Enemy Troops Extender - SephirothSpawn (I love your comment on that one. I always have a hard time deciding which of Seph's scripts is the most useless. xD USE IT, YOU TOTALLY NEED THAT! :V)
Event Collision Detection - SephirothSpawn (His hobby I suppose. Best you don't touch it, nobody knows if it might explode.)
Mapping Layers - SephirothSpawn (I can't see the point. I know, if you have an i.e. SNES emulator, you can turn of mapping layers and sprites and so on, but I never saw any purpose in it. I doesn't even help with debugging maps. =/ Can be added anytime.)
Save Event Locations - SephirothSpawn (Actually, the default save already does what FTS said. -_- The positions are only reseted if you have made changes in the project before you run it again. Print that script down on a paper and burn the paper. While it's burning, delete the script from your HDD.)
Skills Use Element Set - SephirothSpawn (Let's say you have a weapon with elemental attributes Fire and Ice. Thsi skill will adapt them and lauch and Fire/Ice elemental attack. Can be useful if you actually find a purpose. Maybe a Copycat class that has that skill, IDK. =X Add it whenever you want, I'd say. IF you want, that is.)
Sound Interaction System - SephirothSpawn (Yeah, sounds really promising. I remember that somebody (NAMKCOR?) made a script that makes a BGS louder if you get like closer ot an object. You should decide right away if you wanna use it. It will most probably require a lot of extra work if you use it.)
Stat Skills - SephirothSpawn (Do you need that? Then you should add it right from the beginning on and make some extra stuff that will increase the stats so the player can use it before he actually has the level to do so.)
Unarmed Stats & Development - SephirothSpawn (errr...)
Event Icon and Text Display - SephirothSpawn (Actually I don't know how much sense this makes in a non-solid-background-3D game, but if you decide to use it, it can be added at any time. You will just have to do some edits in many events I supposed.)
Perspective Sprites - SephirothSpawn (Something like a pseudo-3D cam? I have one that is for battle nice effect. And yeah, he absolutely didn't make what I was thinking of. Maybe it's better that way. Actually if he did, this would have made a rotating Mode7 script possible. Can be added anytime, I suppose, but it would require some edits in the events.)
State Pops - SephirothSpawn ( -_- I wouldn't use that. CAn be added anytime, though.)
Blue, Geomancy & Level Skills - SephirothSpawn (You have a Blue Magic Skill in Tons of Add-ons, but it works differently. You can use it to "copy" skills from the enemy. I never liked Geomancer, but some people probably do. And yeah, the level divisor skill is gay. Do you actually need some of those? If yes, add the whenever you want, but I suggest from the very beginning, so you know what you will have later in your game.)
Skill Mana System - SephirothSpawn (Too confusing IMO and unecessary complicating things. So this is like adding another SP stat? Unless you have to charge it up differently. But then again, isn't that like almost a limit break. -_- If you need it, go on, but add it from the beginning on, it might make your game inconsistent if you add it later in development.)
Action Encounters - SephirothSpawn (Can add some spice if you want it. I found out that several people are annoyed by random encounter so I made it slightly different in my game. You get a message that you are about to engage into a fight. There's a 20% chance that you can get a choice window whether to fight or not. If you choose not, there's a 50% chance that you don't fight. Additionally I added an option in the Options Menu that allows a default action when you should get that message. My point is that some people could be even more annoyed by this feature. Can be added anytime.)
Battle Simulator - SephirothSpawn (WOW I TOTALLY COULDN'T MAKE A GROUP WITH JUST ONE ENEMY! THANK YOU SO MUCH SEPH! :V)
WorldMap Teleporter - SephirothSpawn (Yeah, sounds like an airship script. Why couldn't he call it FFX Airship script, since it IS a clone. -_- Well... If you have a need for it, go on.)
Battle Escaping - SephirothSpawn (Could be Useful, depending on how it works. i.e. If one character gets away and the rest dies, what happens? Imagine boss fight. You simply get away with one char and battle with the others. You can't lose at all. Not considering the fact that you can make boss encounters inescapable. xD You can add it anytime you think that it's useful for you.)
Battle Leaders - SephirothSpawn (Yeah, can be nice in some cases. Depends on if you need it. I guess it can be added anytime during the development.)
Dynamic Defending - SephirothSpawn (I've seen numerous scripts like that. Couldn't he, like, pick a better name like "Defending Recovering"? -_- Dynamic Defending sounds like one time you take 20% damage, the other time 70%, then 55%, you get the point. Well, it can be added anytime if you feel the need.)
Caldaron's Battle - Caldaron (LOL!)
Language - elbrunito (Oh, I remember that script. Yeah, it was a weird way to make dialogues. Just like FTS said, this can be done easier. I have in my game a variable that is set to which language the game is right now. Then I simply use conditional branches in events and a simply if-else branch in the scripts. I suggest you leave that script in a corner and run away before it wakes up.)
Scene_Map Addition - Tsunokiette (Nice.
If you need it, use it. I know that Tsuno doesn't make crappy scripts).
That's it I guess. Anything else?