What items should be acquirable in-game?
Should we use some Pecry Jackson weapons? Weapons such as Greek fire or Riptide.

Some greek themed weapons are ok. Some other side weapons would fir to.

I did some research. Greeks typically used spears, swords, bows, javelins, and slings.
Shields: Hoplon (wood) and pelte (wicker)
Helmets: corinthian (earliest), phrygian (lighter), chalcidian, and boeotian (heaviest; for calvary troops)

Here's a simple spear inv icon.

That's fine for now. Eventually I want to have higher resolution 16 bit graphics?

You will experience the shitter once you realize that 2D graphics are harder to make then 3D Objects. Unless you have some dedicated talent, you shouldn't try to get better graphics, it will already take up enough time.

As a tip, you want to look up the 3D sprite convertation method, where you create a 3D model and take pictures of it from the side. An advantage is that you can quickly finish all the character poses. As for the disadvantage, depending on your model and art skills, the game will not look as great as an entirely drawn sidescroller. Plus, it will loose the Bit/Pixel-Charm.

You could also consider making your game entirely in that 8-bit pixel style if you lack the skills to do it better. Forcing yourself to draw 16 bit graphics will take forever to finish the game, plus it will probably look pretty bad.

I agree with boatman.

Why? Because when I make graphics for SCP CORRIDORS, either the the lighting doesn't match or it looks like it's attached to the ground instead of another tile.

Luna, if you want I can make this game for you in RPG Maker XP. The game has tons of default tiles, and I'm pretty good at making tiles.

Alright, we'll use 8 bit graphics.

Cridone, if you want to make it in RPG maker, go on ahead. As much as I want to make it in Game Maker, you can do what you want.

You're the creator of the game, you can make it in Game Maker.

Besides, I just noticed that I'm pretty busy.

I'm not surprised. You sign yourself up for a lot of mods and games, so I kind of expected to find you to turn down something at some point.