Need thining down my code/ Finding Players from humanoid?

Find Nearest Player

Unfortunately, there is no easier way I can think of to find the closest Player other than to loop through all of the players. However, you are looping through everything parented to the workspace.

A better way to accomplish what you want is to limit how may times you loop. What we can use is the method of Players GetPlayers in order to look at all the players in the game.

local function findNearestPlayer(pos)
	local closestPlayer = nil
	local distance = math.huge
	for _, player in next, game.Players:GetPlayers() do
		if player.Character then
			if (player.Torso.Position - pos).magnitude < distance then
				closestPlayer = player
			end
		end
	end
	return closestPlayer
end

One Script, All NPCs

A potential improvement would be to use one script to operate all of the enemies. You can set up a loop that creates threads that runs the function used for each character.

Example code

local NPCs -- A list of all NPCs
local NPCFunctions -- A list of all functions for different NPCs

for _, npc in next, NPCs do
	local type -- determined type of NPC (could use a value object in the NPC itself)
	local NPCFunction = NPCFunctions[type]
	spawn(function NPCFunction() end)
end

Example Table for NPCFunctions

local NPCFunctions = {
	["Pirate"] = function() print("arhg!") end
	["Cow"] = function() print("moo!") end
}

One improvement for tidiness would be to put the NPCFunctions in a ModuleScript. You could also define the functions outside of the table to make that easier to read as well.

And if there is any code that is constant across all of the NPCs, you could put it into a function that receives arguments that may be specific to that NPC type (or even another function).

local function Pirate()
	print("arhg!")
end

local function ConstantCode(type, otherFunction)
	print("I am an NPC of type " .. type)
	otherFunction()
end

ConstantCode("Pirate", Pirate)

--[[ Output : 
	I am an NPC of type Pirate
	argh!
]]

Of course this is just one way I conceptualized accomplishing this, so you may find a better way to organize all the data, but making it so that all of these NPCs are controlled with one script will for sure help to improve performance.