I'm not sure what's your strategy here. If you are using a deck with virtually 48 cards (with the cromatich things and proohetic prism) and the
Urza's lands (enabling you to have a lot of mana soon enough) I think you should consider using something stronger, since you have creatures that allow you to resist but nothing really strong enough for the final blow. I would search for stronger artifact creatures like
Darksteel Colossus as creature winning card, and maybe keep somthing of what you already have to resist until then, or add some control cards.
Oh, and maybe you could use
Ulvenwald Hydra or
Primeval titan for land searching, wich would be better than
game-trail changeling (not sure why you are using this card) and you could even use less
expedition map then.
Also,
Mishra's bauble is way better than
prophetic prism I think. You have enough green lands and the chromatic artifacts to have green mana so this card is just slowing you dawn becose of the mana cost.
Mishra's Bauble does
more or less the same for free (exept that you can't use it to get green mana).