Taken from Greg Marques' blog on channelfireball (http://www.channelfireball.com/articles/designer-fun-designing-mechanics/) where he talked about designing new mechanics and suggested this to mimic the feeding frenzy of a shark.

Onto the battlefield from where? Hand, presumably? Or from outside the game? :)

Yes, hand :)

Heh, I saw 'non-lethal' and was reminded of Dungeons and Dragons, and the idea of damage that wears off quickly over time (in Magic-ese, I guess that would be regain one life per turn. Probably involving temporary damage counters.) That, itself, seems like a pretty cool idea.