The control-changing effect doesn't expire if another player gains control of Giant's Grasp (although this is likely to cause it to leave the battlefield because it can enchant only a Giant controlled by the controller of Giant's Grasp)
For the cards available, you can also find foil versions of them, which are slightly harder to find
When a new attacker finally comes back to the Active Spot with multiple Energy attached, its time for Unfezants Downburst again
I really like this deck overall, both in terms of gameplay, and as a big LotR nerd
Picking out the best cards before a set is released is tricky, as it's hard to know how each card synergizes with the rest of the set and within each format
Some recent commanders that might want to consider this card in the 99 include Ellivere of the Wild Court and Galadriel, Light of Valinor