It seems relatively balanced to me, with 2 possible exceptions:
1) with PU, you could do an OTK more easily than with titan since stored damage would get copied (if it doesn't then this isn't a problem though)
2) What happens when a flying version gets lobotomized? Does it never attack? Otherwise you could just wait a few turns and lobo one of these... then BOOM you have a creature with 21 attack.
Concept is cool. It reminds me of an idea I put into the pre-smithy a while back, but never finished up.
http://elementscommunity.org/forum/index.php/topic,40349.0.htmlYour idea is fairly distinct (mine only released a portion of stored damage upon use rather than all at once), but there are enough similarities that maybe the discussion might help here.
Hope you can work all the kinks out. This would make a very fun weapon to have in game I think.
On a somewhat tangent, this would have been a cool entry for the Card Design category of the Forum Brawl this round (round 3) ... We're making mythological weapons.
-On that note... A shameless plug -> Hey everyone, don't forget to vote in the Forum Brawl this week!
http://elementscommunity.org/forum/index.php/board,483.0.html