Thanks a lot for releasing a demo!
I've been playing it for about 20 minutes, and here's my feedback so far.
First of all, congratulations for the project. I'm totally impressed by your demo, it feels like the basis of a commercial-grade game (much like Anguna on GBA).
The graphics are beautiful, the music is cool, and the engine / core gameplay is solid. You successfully recreated the whole gameplay of the "Secret of" games, up to the famous ring menu. I was astounded to find that everything is working: changing characters, getting new weapons, setting the AI of the "following" character, trading weapons between characters, dialog system with PNJ, enemies, saving/loading, etc. The scrolling system is also very well done. Kudos, all of this is really impressive.
I can not imagine how long you have spent coding all this.
The game is also quite challenging in its current state, with quite a lot of maps / content for a first demo. I managed to recruit the "sorceress" character, but I didn't find anywhere to go after that: is this the end of the demo, or is there any additional content that I missed?
I also have some suggestions / personal feedback that may or may not help you:
- I find that the player character moves too slowly. I died 3 times in the demo and had to start it all over again, and, in my third attempt, I really wished that there was "run" button (like in Secret of Mana) to run through the maps I already explored. Also, the enemies moves way faster than the player, so it's really hard to avoid them when they attack you. Personally, I would increase the "walking speed" instead of adding a running button, so we can both avoid them more easily and have more fun exploring the maps.
- There is a slight delay between the "attack" button and the actual attacking frame. It makes the player vulnerable during a short windows every time he attacks, due to the animation frame where the hero "charges" his punch / sword / dagger attack. I'll remove this frame to display the "sword / dagger / punch" frame instantly after a button press, or at least I'll reduce its duration, because it feels too slow for me in this demo.
- The sprites (PNJ, enemies, chests) appears / disappears from the screen before being actually "out of the screen". I think that you only test their top-left position after a scrolling to check whether they need to be displayed / hidden. That leads to some "sprites teleportation" sometimes. It's a not deal breaker, but it'll look more polished if the sprites actually went offscreen before being hidden

.
- I won't spoil it for everyone else, but I did enjoy the little "puzzle" in this demo (it took me some time to figure it out how to go to screen where you can recruit the sorceress

)
P.S.: I tested in on BSNES set in PAL (50Hz) mode, without any particular filter.
Once again, congrats for all the great work. I really hope you can complete it in 2018. We got Sydney Hunter a few days ago, so if we also have your game released too, that'll be a very good year for SNES homebrews!