Modded trinket support (example mod)

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

local moddedCos = {		-- keeps track which trinket is in the player posession
	YourTrinket = false			-- ex. BloodyCobweb = false
}

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

-- change if the costume gets applied on pickup or by smelting
function Mod:setTrinketCostume(consol,para)
	if consol == "onPickup" then		-- global. regulates when a trinket costume is applied
		if moddedCos.YourTrinket == true  then
			ctc:SwitchCostumeRequirement(TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET) 	-- gets called if the costume gets applied by picking up the trinket. Also removes the costume until it's applied again.

			if switchTrinketBoolean == true then		-- got set to 'true' in the function above
				moddedCos.YourTrinket = false		-- reset moddedCos so that the costume can be reevaluated/applied again
				switchTrinketBoolean = false		-- reset switchTrinketBoolean for a later use
			end
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_EXECUTE_CMD, Mod.setTrinketCostume)

function Mod:onNewRun(bool)
	-- reset all moddedCos. variables to false at the begin of a new run

	if bool == false	-- is false on the start of a complete new game
	and trinketCostumesMod then
		moddedCos.YourTrinket = false
	end
end
Mod:AddCallback(ModCallbacks.MC_POST_GAME_STARTED, Mod.onNewRun)

function Mod:onModdedCostumeUpdate(_)

	-- check if trinket costume mod is active
	if trinketCostumesMod then
		for i = 0, (game:GetNumPlayers() - 1) do
			local player = Isaac.GetPlayer(i)

			if player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET)	 -- still have to check if the player has the trinket
			and moddedCos.YourTrinket == false then
				-- add the costume
				ctc:AddTrinketCostume(player, TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET)	-- applies the costumes. On smelting or pickup dependin on 'onPickup'
				-- change the moddedCos. boolean
				if switchTrinketBoolean == true then		-- got set to 'true' in the function above
					moddedCos.YourTrinket = true		-- the player now has the costume
					switchTrinketBoolean = false		-- reset switchTrinketBoolean for a later use
				end
			end
			if (not player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET))
			and moddedCos.YourTrinket == 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)
				moddedCos.YourTrinket = false			-- needs to be reset so that the costume could be...
														-- applied again in the same run
			end
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_POST_UPDATE, Mod.onModdedCostumeUpdate)