Now that I've created a few TI-89 Basic programs, I really want to write an RPG. This is a plan for one I might write.

The character will navigate through 8x16 tilemaps, which will be stored in a list of strings (one string per 5x5? map world). A quick calculation shows 128 characters per map*25 maps/world=3,200 characters. Therefore I will probably be writing the strings on an editor. Another method is to use multiple archived strings named, perhaps, map0, map1, etc. A space would be a spot you could walk on, L a wall, and 0-9 and perhaps a few more characters symbols for people. Greek characters might be quest items.

Now, quests. Each quest will have an ID from 0 to n-1. The types for each objective will be fight, fight and collect, collect, and talk. Each quest has one or more objectives (ex. fighting 3 of one enemy, 5 of another, and coming back to an NPC).
Fight: {enemy id, number, 0}
Fight and Collect: {enemy id, number, probability}
Collect: {item id, 0, 0}
Talk: {person id, response, 0}
Each NPC has a unique ID; I am thinking about storing their positions in a list, where every 5 entries look like {world, global row, global col, local row, local col} where the "global" coordinates describe which map in the world it is and the "local" coordinates describe where in the tilemap the person is. I could compress it to {world, map#, localcoords} or {25*world+map#, localcoords} or even {128*(25*world+map#)+localcoords}. For speed, however, I would use {w,m#,lc}.
The fighting system will not involve "cards" as in Sunrise 3. There will be a screen showing ASCII representations of the player and the enemy and a custom menu asking for an action (Fight, Magic, Item, Pass, Run). Each enemy has an ID as well, as well as a list associated with it, containing the enemy data (health, mana, lvl, can fight, can magic, can item, can pass, can run, stun rds, poison, xp reward, gold reward, # of spells, spell 1, ...). "Fight," as well as each magic will have a list consisting of action, arguments, action, arguments, etc. Some actions will be Attack(type, min, max), Heal(min, max, 0), MHeal(min, max, 0), ModUserAtk(fact, 0, 0), ModEnemyAtk(fact, 0, 0), ModUserDef(fact, 0, 0), ModEnemyDef(fact, 0, 0), Poison(amt, 0, 0), Stun(turns, 0, 0). Both players and enemies can use the same spells and there will be different programs for players to cast spells and for enemies to cast spells.
Shops will have a commond program available that will work with all shops, taking a list argument. Since For() loops are disallowed in ToolBar...EndTBar statements, I would be using a custom menu with up to 8 options, not including the one to return.

I'd like your feedback on this plan, thanks in advance!

Umm... how many times slower approximately?

Yes, I am aware of how lists work on the TI-89. That's why I'll use strings for the maps. Also, the lists I am using will probably be small.

Yes, I wrote a few programs in C, such as here.

Edit: I also have an elaboration on the map generation. A segment of the large string corresponding to the section of the world is copied to the RAM, so quest items can be removed from the map when the player collects it. Do you know a decent TI-89 Basic editor?

Daisuke Basic Edit, or TI-Edit ?

More on NPCs...
Each NPC has a default phrase to say when you have no quests from him/her, and have a lists of quests to give. Each quest is represented by a list, all stored in a function, and the requirements are stored in another function, called qreqs(id). Also, the locations for the NPCs will be located in npc0 ... npc9.
The shop program will use a list containing global item ids (ex: shop({1000,1001,1002,2003,3002,4005})).

Edit: I might also do a port of one of DJ_O's RPGs, if that's OK with him.

Edit 2: If TI-Basic turns out to be too slow, then I might implement some C. Also, I've thought about the name. I might name it Sunrise 1.1 or Moonscape (name of an abandoned computer project).