Updated Modded Trinket support 2

local Mod = RegisterMod("yourModName", 1)
local game = Game()

-- trinkets
TrinketType.TRINKET_YOUR_TRINKET = Isaac.GetTrinketIdByName("Your Trinket")		-- your trinketId
-- costumes
Mod.COSTUME_OF_YOUR_TRINKET = Isaac.GetCostumeIdByPath("gfx/characters/yourtrinketscostume.anm2")	-- your costumeId


function Mod:setModdedTrinketCostume(consol,para)
	if OnPickupSwitch(consol) then			-- takes "onPickup" and checks if it's state is 'true'.
							-- If so, the it will return true. Otherwise it will return false
		for i = 0, (game:GetNumPlayers() - 1) do
			local player = Isaac.GetPlayer(i)
			local playerData = player:GetData()
			if playerData.YourTrinketName == true  then
				if ctc:GetHeldTrinkets(player, TrinketType.TRINKET_YOUR_TRINKET) then	-- check if the player holds the trinket in one of the..
														-- trinket slots (returns true or false)
					player:TryRemoveNullCostume(Mod.COSTUME_OF_YOUR_TRINKET)	-- remove costume
					playerData.YourTrinketName = false
				end
			end
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_EXECUTE_CMD, Mod.setModdedTrinketCostume)

-- on post peffect update
function Mod:onModUpdate(player)

	local playerData = player:GetData()		-- if you already assigned a variable to player:GetData() that's fine. Just make sure to use it instead of playerData

	if game:GetFrameCount() == 1 then
		playerData.YourTrinketName = false		-- saves and keeps track if the player has picked up YOUR trinket | ex. playerData.BloodyCobweb
	end


	if trinketCostumesMod then		-- trinket costume mod is active
		if player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET)	 -- still have to check if the player has the trinket
		and playerData.YourTrinketName == false then
			-- add the costume
			if onPickup == false then 		-- global variable which decides when the costume gets applied
				 if ctc:TrinketIsSmelted(player, TrinketType.TRINKET_YOUR_TRINKET) then     -- specific function which checks if the to evaluated trinket is smelted
											     -- returns 'true' or 'false'
					-- costume would get applied by smelting the trinket
					player:AddNullCostume(Mod.COSTUME_OF_YOUR_TRINKET)

					-- set moddedCos. to true
					playerData.YourTrinketName = true
				end
			else
	 			if player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET) then
					-- costume would get applied by picking up the trinket
					player:AddNullCostume(Mod.COSTUME_OF_YOUR_TRINKET)

					-- set moddedCos. to true
					playerData.YourTrinketName = true
				end
			end
		end
		if (not player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET))
		and playerData.YourTrinketName == true then				-- check if the costume needs to be removed
			-- remove the costume
			ctc:RemoveTrinketCostume(player, TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET)
			playerData.YourTrinketName = false
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_POST_PEFFECT_UPDATE, Mod.onModUpdate)