This script was only inspired by Lemmy's version and doesn't have all the features his did. To help you decide which one to use, here's a list of features exclusive to each:

Features exclusive to Lemmy's script:

• NPCs can be placed off the 16*16 pixel grid and function fine
• You can make any FFC solid (Although this doesn't mean you can't break through them)
• NPCs have a nifty overhead effect when you walk behind them
• NPCs can move about and still be solid

Features exclusive to my script:

• You can have NPCs appear based on items as well as disappear
• You can have NPCs run scripts when you talk to them
• You can have an icon appear above Link's head when you can talk to an NPC
• You can safely use guard NPCs to block off areas

Update 3/23/2015:
I've hopefully fixed a bug that caused ZC to crash sporadically upon entering the screen. If you still experience crashing after updating the script or any other odd behavior, please send me a PM.

Update 2/26/16:
I've added a small fix to prevent screens that share the same layer screen from carrying over solidity from NPCs onto other screens. Since this could potentially break some people's setups, there's a constant to turn it on or off.

Update 1/13/18:
Added a an argument for FFC script calls on the more complex version of the script and the option to wait for called FFC scripts to finish before resuming.

Update 3/12/19:
Added an exception for the DialogueBranch addon even if NPCSCRIPT_WAITS_UNTIL_SCRIPTS_FINISH is turned off. Added a setting to prevent ItemCheck NPCs from disappearing immediately if you get an item on the same screen.

Update 12/1/21:
Rearranged some stuff in the script. Added checks for Link's current action, as well as better compatibility with flippers and roc's feather.
Update 12/1/21: Rearranged some stuff in the script. Added checks for Link's current action, as well as better compatibility with flippers and roc's feather.

Settings Constants:

• RESET_NPC_LAYER_ON_ENTRY: If set to 1, the script will reset NPC solidity when entering a screen. This fixes screens that share layer screens.
• NPCSCRIPT_ITEMCHECK_ONLY_UPDATES_ON_SCREEN_ENTRY: If set to 1, NPCs that disappear when Link collects an item on the same screen won't disappear until you scroll off the screen.
• NPCSCRIPT_WAITS_UNTIL_SCRIPTS_FINISH: If set to 1, FFC scripts run by the NPC script will interrupt the NPC script running until they finish. This prevents talking to the NPC while these scripts are running.

Full NPCScript:
This is the original full NPC script with all the fancy features.

Constants:
Set LAYER_NPC to 1 or 2 depending on which layer you want to use for NPC solidity. (Or you can use -1 to use it like an old fashioned NPC script where you set the solidity yourself)

Set CMB_NPC_HIDDEN to an invisible combo with no solidity.

Set CMB_NPC_SOLID to an invisible combo that's fully solid

Set LAYER_NPC_CANTALK, CMB_NPC_CANTALK, and CS_NPC_CANTALK to the layer, combo, and CSet the speech icon should appear in.

Placement:
Place FFCs on the 16*16 pixel grid. You can select View->Show Grid or press the ~ key to make the grid visible.

Be sure that you have the Run Script at Screen Init FFC flag checked and the Messages Freeze All Action and Messages Disappear quest rules checked.

FFC Arguments:

• D0: Set this to the string that should play when you talk to the NPC.
• D1: Set this to the item that makes the NPC disappear. Make the number negative to make the NPC appear when you have the item instead.
• D2: Set this to the type of NPC it will be:
  • 0 - None - Does nothing special
  • 1 - Face Link - Faces Link when you get close (the FFC's combo should be the first of four facing: Up, Down, Left, Right)
  • 2 - Guard H - Follows Link on the X-Axis
  • 3 - Guard V - Follows Link on the Y-Axis
• D3: Argument 1 for the NPC's movement type:
  • None - Does nothing
  • Face Link - Default direction the NPC should face (You can set this to 4 to give it a custom default state)
  • Guard H - Min X position in tiles
  • Guard V - Min Y position in tiles
• D4: Argument 2 for the NPC's movement type:
  • None - Does nothing
  • Face Link - Distance in pixels at which the NPC will turn to face Link
  • Guard H - Max X position in tiles
  • Guard V - Max Y position in tiles
• D5: Set this to 1 if you don't want the NPC to be solid.
• D6: Set this to a number greater than 0 to call that script when you talk to the NPC
• D7: Argument D0 for the FFC script called by D6

NPCScript_Simple:
This is a simplified version of the original script with the extra stuff stripped off. It doesn't do automatic solidity, moving NPCs or appearing/disappearing NPCs, but it's more flexible for attaching scripts to because it can pass all its extra arguments to them.

Constants:
Set LAYER_NPC_CANTALK, CMB_NPC_CANTALK, and CS_NPC_CANTALK to the layer, combo, and CSet the speech icon should appear in.

Placement:
Place FFCs on the 16*16 pixel grid. You can select View->Show Grid or press the ~ key to make the grid visible. Since this version doesn't have the automatic solidity, you'll have to place down solid combos under it yourself.

FFC Arguments:

• D0: Set this to the string that should play when you talk to the NPC.
• D1: Set this to a number greater than 0 to call that script when you talk to the NPC.
• D2-D7: If you call a script with D1, these work as that script's D0-D5.

TradeSequence:
This is an example of an add-on script that can be called by the simplified NPC script. It makes an NPC that takes one of your items, gives you a new one with a hold up animation, and remembers that you've traded with it.

Constants:
Set D_TRADE to an unused Screen->D value 0-7 if you have other scripts using Screen->D.

Setup:
Instead of being placed on the screen as an FFC, this script is called by another FFC using the NPCScript_Simple script. Set D1 on that FFC to this script's slot and D2-D6 to this script's D0-D4.

FFC Arguments:

• D0: The item ID of the item to check for in the trade.
• D1: The item ID of the item to give in the trade
• D2: The string that plays when the player doesn't have the required item
• D3: The string that plays when the player has the required item
• D4: The string that plays when the player talks to the NPC again after making the trade

This script uses ffcscript.zh in addition to std.zh.