Okay, how about this: the black one is an auto-include, and is strictly better than Ancestral Recall. Yes there are scenarios where you're at less than 10 life. You know what causes that? Yawgmoth's Bargain and Channel. If you resolve either of those two cards, you win the game.
The green one is solid but not spectacular; the effect isn't good enough for the drawback.
The blue one is fine, but uninspiring.
The red one is pretty poor, especially since it's competing with a lot of effects at the same level. Also, it should be "You win all flips."
The black one: Yeah, right.
The white one is especially random, why does it not empty their mana pool? And not blocking effects are very red, not white.
Urza: Never ever. Especially since you had to tack on a lot of useless effects (life gain, making wurms) in order to get all 5 colors.
The mechanic is fairly uninspiring, it can only be degenerate or worthless, and that sort of effects go against the flavor of UGW.
Concerning the black one, would an additional cost of "Discard your hand, then remove your graveyard from the game:" be better? This way a combo deck would have a far tougher time abusing Will.
The green one. Would it be better as a 7/7, 8/8?
I know the red one is poorer in power level then the rest, however this hasn't stopped cycles from being printed before (the Kamigawa dragons as an example....or for that matter the Exodus Oaths).
The white one I had trouble with, which is why its rather random. The reason the mana pool didn't empty was because I was trying to make it so that an opponent would have to use the element of suprise (i.e. with a card in hand) in order to stop the opponent's attack. The flavor of the white one was supposed to be somewhat of a large-scale well-planned thought out attack in which soldiers invade using the attacking army uses all its resources to take out the opponent's resources. Put another way it should resemble the magic equivalent of D-day.
Urza: The critiques on this one are pretty good. I'll drop this one.