I haven't played this particular Madou Monogatari game (I hate dungeon crawlers, and the language barrier doesnt help either), but Bayoeen is the "ultimate" spell in literally every iteration of the series - even in Puyo Puyo.
On the Saturn MM game, it does non-elemental damage to all enemies. On the SNES game, it was a happiness bomb that made enemies forget about attacking you for a while.
There are a few japanese sites with huge character encyclopedias for Madou Monogatari, the easiest to navigate (that I know of) is this:
http://suwa3.web.fc2.com/data-kan/index.html
Do note that it stuff written about every MM game, not just the Megadrive one.
Use this tool for translation, it is much better than the crappy google translator:
http://www.ocn.ne.jp/translation/?tool3
Also, I can help translating the character names if you need. The "girl with the broom" is probably called as Witch, if it is the blonde little girl with blue outfit. You can tell the character names are imaginitive.