When Elizabeth said Spellsteal was crazy cheap fun, she wasn't kidding. Spellsteal is the new level 70 Mage spell that steals a beneficial magic effect from an enemy (it only works sometimes, but being as my mage is only around 25, I couldn't tell you offhand exactly where it works and doesn't). Stiil, as the video shows, a mage with spells he's not really supposed to have can get a little crazy.
Now, I'm also told this no longer works (most likely this is an old movie, and Spellsteal was tweaked to not work with this AoE spell). But I'm guessing we're just scratching the surface so far on all the ways Spellsteal can be used to full effect.