So I saw many suggestions asking for a Custom Creatures list and the ability to add them as ingredients, which I understand is hard to code. I think an easier, less complex that can be used at least for a placeholder is to have "Custom options" while choosing ingredients. When you choose ingredients, at the end of the list popped out you will have: Custom Common, Custom Rare, Custom Super Rare, Custom Legendary, Custom Tournament and Custom VIP (Custom Star and Custom Super Star?). For each option a blank icon of the rarity chosen will be generated as the ingredient icon, and you can add, move and resize images inside. Same goes for choosing base ingredient for S-hybrids. And for S-DNA there will only be a "Custom" option, and you can pick it to add, move and resize images.
