Memory addresses less than 0x100 tend to be used for temporary or scratch calculations.

Each of 0x04E0-0x04E6 are bitfields which represent current Story Progress.

Sprite data is stored in more or less the same sort of structure between Nasir and NPCs and Enemies and so on. It's a 0x40 length record.

At two points in the game you are burdened with needing to escort an NPC. While escorting an NPC the exits are locked until the follower is considered close enough to the door. Whether or not to let you through the door is mostly determined by the 0x10 flag, which is set based on the NPC's location relative to the camera. This bit is set when the NPC's camera X Coord is in the range [64, 192] and the camera Y Coord is in the range [80, 176].

These start at 0x20 = 32. I do not know the reason for this yet.

These are located in 0x4D0 through 0x4D7, each bit corresponding to a specific item, spell, or equipment. Unlisted values are unused; however, they are not invalid, in that they survive a save and restore and do not cause bad interactions as far as I am aware.

Resistances are listed in the form of 4 numbers, 0-F, which is a bitmask that determines which spells effect the enemy. Level 1 spells check the first bit, level 2 check the second and so on. So if an enemy has a 0, then no spells affect it, if the enemy has an F then all spells affect it, E then spells Level 2 or higher affect it, C level 3 or higher. The order is given by Lightning, Water, Wind, Fire. So FC0E is fully vulnerable to jLightning and will take damage from level 2 or better Fire spells, vulnerable to level 3 or better Water Spells, and completely immune from Wind spells.

Room Sprite Data is located at ROM address 0x859552, in a packed array of 0xFFFF terminated lists. Each entry is formatted as this structure

It is referenced by a mostly unexplored Room Metadata struct, that has the 24-bit pointer at offset 0x2B. Room Metadata is stored in the ROM at 0x85B2DF, and each entry is 0x38 bytes long.

A table at 0x858059 contains pointers to room exit data. The data is formatted as:

struct RoomExit {
    int exitReducedXCoord;
    int exitReducedYCoord;
    int destinationXCoord;
    int destinationYCoord;
    char destinationRoomID;
    char destinationFacingDirection;
    char field_A;
};

Where the reduced coords are the coordinates divided by 32. field_A might have something to do with perhaps cutscene handling. I am not sure yet. The list is terminated with 0xFFFF. The list has some oddities, for instance, Poper Church Basement should normally only have two exit tiles, but it doesn't have a proper list termination, so it also inherits the Siegfried Castle Entrance exit tiles. This could be an interesting shortcut if some way were found to activate these exits.

Nasir's attempted movement direction gets mixed in with the RNG at 0x81814B by simply adding it to 0x03B5, giving the player a way of controlling the RNG a little bit. However, these numbers are rather small (-1, 0, 1, 2, 3), additionally, because Manhattan geometry, there are several different equivalent paths to go to a specific point; however, they will all add the same amount overall. The ways to change this are via an delay, and via cutting a corner more or less. Phantom Hill Summit shares exits with Clouds, and Samson's Room shares exits with the unused room ID.

Every time an RNG value is needed 0x809848 ("GetNextRNG") is called.

This function does roughly the following:

acc = $3B5 + 1;
$3B4 = acc;
$3B5 = 5 * acc;
$3B4 = $3B5 * 16 | $3B5 / 16; // nibble swap
return $3B4;