Lujo is right. If you're under the effect of 'Sprit Sword' you could trigger it a second time, but wont get the damage buff.
Before that patch one could really abuse it, here is the link to the topic:
http://www.qcfdesign.com/forum/viewtopic.php?f=3&t=2417Goblin was nice due to the xp from conversion, with it one could refresh mana. But orc gave in the end more damage (422 at lvl1

). Think human should have worked too. Best result i got in 'Magma Mines':
One shotting magic immune boss at lvl 1. Then burning the physical immune (only one fireball). Then again using all ressources for 'Spirit Sword' stacking to kill the last boss (don't remember if it was also a one shot).
Somehow is miss it that 'Spirit Sword' doesn't stack. Sometimes 2stacks would be nice. But the massive stacking which i did in the three runs (linked in the above link) were quite broken.
Someone had the idea to use B2P for even more spells cast, think with that approach the damage would have get quite ridiculous