Board Thread:General Discussion/@comment-25550913-20141018005631/@comment-25120551-20141020201609

You would normally only merge a joker in order to break the level limit for a spirit. As in, when you first get a Super Rare spirit, it can only advance to level 25. Once you max out the levels you need to use another copy of that spirit or use a Joker of the same element and it will open it to advancing higher up. For supers, they will advance an additional 10 levels for every level break up to 65.

I prefer to save them for really hard spirits to get. Such as event spirits like Verdandi who everyone and their mom want and those giving them typically demand a lotto get it, so its easier to use a joker and save yourself the need for trading for an extra event spirit and just use the joker and save the copies for a pure merge to bump the stats up, or trade off if you want other stuff.

Rule of thumb for me is, if the spirit is easy to come by, whether its summoning or trading, its not worth using a joker on unless you cant wait to advance it up.