To fight a Bacura, the big solid Mana blocks in the Toize Mines, go to the last room, where you get the ore. There will be a one-eyed monster in there. fight it. Sometimes it will be a couple of Stone Golems with some other monsters, and
sometimes it will be a Bacura. Just run away if it is not a Bacura and re-encounter it. The Bacura has 255 HP and you can only drain one. Also, it disappears after thirty seconds.