canto-namespace-protocol/src/Namespace.sol#L110
    function fuse(CharacterData[] calldata _characterList) external {
        uint256 numCharacters = _characterList.length;
        if (numCharacters > 13 || numCharacters == 0) revert InvalidNumberOfCharacters(numCharacters);
        uint256 fusingCosts = 2**(13 - numCharacters) * 1e18;
        SafeTransferLib.safeTransferFrom(note, msg.sender, revenueAddress, fusingCosts);
        uint256 namespaceIDToMint = ++nextNamespaceIDToMint;
        Tray.TileData[] storage nftToMintCharacters = nftCharacters[namespaceIDToMint];
        bytes memory bName = new bytes(numCharacters * 33); // Used to convert into a string. Can be 33 times longer than the string at most (longest zalgo characters is 33 bytes)
        uint256 numBytes;
        // Extract unique trays for burning them later on
        uint256 numUniqueTrays;
        uint256[] memory uniqueTrays = new uint256[](_characterList.length);
        for (uint256 i; i < numCharacters; ++i) {
            bool isLastTrayEntry = true;
            uint256 trayID = _characterList[i].trayID;
            uint8 tileOffset = _characterList[i].tileOffset;
            // Check for duplicate characters in the provided list. 1/2 * n^2 loop iterations, but n is bounded to 13 and we do not perform any storage operations
            for (uint256 j = i + 1; j < numCharacters; ++j) {
                if (_characterList[j].trayID == trayID) {
                    isLastTrayEntry = false;
                    if (_characterList[j].tileOffset == tileOffset) revert FusingDuplicateCharactersNotAllowed();
                }
            }
            Tray.TileData memory tileData = tray.getTile(trayID, tileOffset); // Will revert if tileOffset is too high
            uint8 characterModifier = tileData.characterModifier;

            if (tileData.fontClass != 0 && _characterList[i].skinToneModifier != 0) {
                revert CannotFuseCharacterWithSkinTone();
            }
            
            if (tileData.fontClass == 0) {
                // Emoji
                characterModifier = _characterList[i].skinToneModifier;
            }
            bytes memory charAsBytes = Utils.characterToUnicodeBytes(0, tileData.characterIndex, characterModifier);
... 
            bytes memory charAsBytes = Utils.characterToUnicodeBytes(0, tileData.characterIndex, characterModifier);
        string memory nameToRegister = string(bName);
        uint256 currentRegisteredID = nameToToken[nameToRegister];
        if (currentRegisteredID != 0) revert NameAlreadyRegistered(currentRegisteredID);
    function testFailMintSameCharacterIndex() public {
        address user = user1;
        note.mint(user, 10000e18);
        endPrelaunchAndBuyOne(user);

        uint256[] memory trayIds = buyTray(user, 3);
        vm.startPrank(user);
        note.approve(address(ns), type(uint256).max);
        Namespace.CharacterData[] memory list = new Namespace.CharacterData[](
            1
        );
//      fuse tile with fontClass=8,characterIndex=1
        list[0] = Namespace.CharacterData(trayIds[1], 4, 0);
        Tray.TileData memory tileData = tray.getTile(trayIds[1], 4);
        console.log(tileData.characterIndex);//1
        console.log(tileData.fontClass);//8
        ns.fuse(list);

//      fuse tile with fontClass=4,characterIndex=1
        list[0] = Namespace.CharacterData(trayIds[2], 3, 0);
        tileData = tray.getTile(trayIds[2], 3);
        console.log(tileData.characterIndex);//1
        console.log(tileData.fontClass);//4
        vm.expectRevert(
            abi.encodeWithSelector(Namespace.NameAlreadyRegistered.selector, 1)
        );
        ns.fuse(list);
    }
-            bytes memory charAsBytes = Utils.characterToUnicodeBytes(0, tileData.characterIndex, characterModifier);
+            bytes memory charAsBytes = Utils.characterToUnicodeBytes(tileData.fontClass, tileData.characterIndex, characterModifier);
