For some reason that original link wasn't working, here's an updated one:
http://www.sega-saturn.com/saturn/other/may-n.htm

And for posterity:
May 21, 1996
Mystaria--Riglord Saga--Blazing Heroes
Mystaria's new name is now Blazing Heroes. As previously mentioned Sega had problems with Copyright violations with the name Mystaria, they were forced to pull the game off of store shelves. It turns out that the Japanese name Riglord Saga also posed some copyright problems, so they've come up with a brand new name. Please note: as reported earlier Sega and TSR came to an agreement that is allowing Sega to sell off their remaining stock of Mystaria
information from IG Online
I've got a complete Blazing Heroes, and a loose copy (both found out here in CO), and a retro game store near me also has a copy of Blazing Heroes they want like $40 for. However, when I grew up in IL I only knew it as Mystaria, so maybe different regions had better chances of getting stuff. This is actually an oddly pertinent thread, since I only really learned that these were the same game like a couple months ago, funny since I've been collecting Saturn games for awhile.