Here is some information on the Mysterious Well. It is a boss fight that 3 minor minions and has changing bosses and minions. Boss also cheat. So far I have been in here 2 times. One boss is Death. His cheat is any positive charms you put on yourself or team mate he steals. So fire and life you two are out of luck when it comes to using the elemental/spirit blade and same with the shields. Now another boss I fought was Ice. His cheat was every time you heal yourself or a teammate he will use the normal fire move Link. Which is considerably weak. If you heal yourself/group he puts the Link on you but heal single teammate he puts the link on that teammate. Now I am pretty sure there are many different bosses in this area so I will Update this message when I have more information on the different bosses.
