my attempt

		-- check if the player is flying and has the Bat Wing trinket (Bat Wings bug fix)
		if player:HasTrinket(TrinketType.TRINKET_BAT_WING) then
			if player.CanFly
			and costumeTr.BatWing == true then	-- player has the trinket / trinket costumes get applied
				-- set the playerData
				if playerData.Ctc_HadFlight == nil
				or playerData.Ctc_HadFlight == false then	-- in case this got already check once before
					playerData.Ctc_HadFlight = true

					-- remove the Body 0 costumes
					player:TryRemoveNullCostume(Mod.COSTUME_CANCER)			-- Cancer
					player:TryRemoveNullCostume(Mod.COSTUME_CANCER_ALT)
					player:TryRemoveNullCostume(Mod.COSTUME_MAGGYS_FAITH_MALT)	-- Maggy's Faith for Maggy
					player:TryRemoveNullCostume(Mod.COSTUME_THE_LEFT_HAND)		-- Left Hand
					player:TryRemoveNullCostume(Mod.COSTUME_RIB_OF_GREED)		-- Rib of Greed
					player:TryRemoveNullCostume(Mod.COSTUME_LOCUST_OF_WAR_AFRAID)	-- Locust of War
					player:TryRemoveNullCostume(Mod.COSTUME_LOCUST_OF_WAR)
				end

			elseif player.CanFly == false		-- only triggers if the player doesn't have flight,
			and playerData.Ctc_HadFlight == true		-- but had flight once before
			and costumeTr.BatWing == true then		-- and should have the small bat wings

				-- resets the costumeTr so that the costumes can be reevalauted
				costumeTr.Cancer = false
				costumeTr.MaggysFaith = false
				costumeTr.TheLeftHand = false
				costumeTr.RibOfGreed = false
				costumeTr.LocustOfWar = false

				-- reset for .Ctc_HadFlight the next use
				playerData.Ctc_HadFlight = false
			end
		end