What is this error

[GodLikesYou (john)]

local playerlist = game.Players:GetChildren()
local dmg = {10}

local metatable = {}

metatable.__add = function(t, t2)
	for i, v in pairs(t) do
		local character = v.Character or v.CharacterAdded:Wait()
		local humanoid = character:FindFirstChild("Humanoid")
		humanoid.Health += -t2[1]
	end
	
	return "Damaged"
end

local function UpdatePlayers()
	playerlist = game.Players:GetChildren()
end

game.Players.PlayerRemoving:Connect(function()
	UpdatePlayers()
	setmetatable(playerlist, metatable)
	print(playerlist + dmg)
end)

the script damages the players but this error pops up everytime someone leaves

[itsBreakon (breakon)]

my old response which i think is wrong

Seems like this is being caused by your CharacterAdded:Wait(), the engine isn’t going to wait to clean up a player instance so your code can finish running.

To put it simply, your code is attempting to yield and delay the C code that is trying to clean up the player instance which the engine obv doesn’t like. To fix this just don’t yield in your __add metamethod, or just don’t call it when a player is leaving.

New response: pretty sure you can’t yield in metamethods

[nothing_1649 (gom_a)]

in short, metamethods are never permitted to yield

[GodLikesYou (john)]

how would I access the character when using metatables

[nothing_1649 (gom_a)]

your CharacterAdded:Wait() is causing the issue, consider referencing the character elsewhere

[itsBreakon (breakon)]

Check if the character is already loaded for that player, if it isn’t then skip over them. You can’t yield in metamethods