Some cards are still more powerful or efficient than others, but the balance of mana costs keeps things in relative check throughout the course of a game
If the spell that's copied is modal (that is, it says "Choose one " or the like), the copy created by Jin-Gitaxias's first ability will have the same mode or modes
Each opponent will know the choices of previous players in turn order before making their own choices
Hell make it for you any time an opposing creature dies, and also grow when you sacrifice your Food or Blood tokens
It's possible to use him to shoot down creature decks, or players can use his Hadoken to be more aggressive by effectively doubling his damage each turn
Its also a way to guarantee your reanimation targets are in a zone thats difficult to interact with for your opponents outside of dealing with Currency Converter directly, which some colors cant do easily