For typical Sealed Deck, you'll get one Tournament Pack of COK and Three Boosters of BOK. This means there may be a chance of getting multiples of Uncommons.
I never got Umezawa's Jitte during our Sealed Deck and never faced one with it, but it looks powerful, when combined with evasion creatures. Come to think of it, if you attach it to a double striker, you get 4 counters.
This card really pairs well with Rend Flesh, and it also combos well with red burn. Betrayers is turning out to be a solid set to strengthen Kamigawa block.
This card would have good synergy with Samurai decks (having Bushido), since you can choose which creatures to block. But don't plop this down if you can't deal with flyers.
You can replace the beacon of tomorrows with the very under-used Beacon of Immortality, since you'll easily get the mana to cast it (making you a little bit harder to kill).
To counter a spell, you need to remove a card with the same converted casting cost. In effect, you're trading off two cards for one. If you're playing a Blue Control deck and your opponent casts a 2-cost spell, would you pitch your Mana Leak and this Shoal to counter? I guess not. If your opponent casts a 3-cost spell, would you pitch your Hinder (or Thoughtbind) and this Shoal to counter? You'll just cast one of the two. Blue should be the master of card advantage, and this card just doesn't help.
And I agree with the question on how will it stop "Tooth and Nail"?
The rats should be improved with BoK. The Inquest article indicated that we'll be having "Rat Ninjas". As for tournament-level Rat decks, let's wait and see.
With the Genju's, WOTC is really pushing enchantments for tournament play. First they gave us the Hondens (which are not too playable), then they turn around and give us the playable Genju's (but we still need to wait and see the other cards). These would be very good in the late game, when you have lots of mana and spare lands, but with Raffinity, there is no late game. Well, at least, this would give players a blocker to stall Raffinity.
Ideally, the Shoals should work using each color's "specialty". Blue is for countering. Red is damage. Green is creature pump, etc.. But since WOTC already gave Red creature pump, it's quite difficult to speculate what Green's shoal will be. For White, it could be life gain (looking at the beacons and the pulses in mirrodin block). And For Black, it could be tutoring (like the bringer) or reanimation (like the beacon).
This card is not really as good as advertised. The main strength of Force of Will is that you do not need mana to cast, just a blue card and loss of life, meaning you can cast it on your first turn. This card has double blue and you still need to remove a blue card. For Kamigawa block, unless Betrayers has another hard counter, Hinder is still the best.
I never got Umezawa's Jitte during our Sealed Deck and never faced one with it, but it looks powerful, when combined with evasion creatures. Come to think of it, if you attach it to a double striker, you get 4 counters.
But knowing Wizards, probably the card would be too powered-down to be useful. Look at Konda's and Hisoka's cards.
To counter a spell, you need to remove a card with the same converted casting cost. In effect, you're trading off two cards for one. If you're playing a Blue Control deck and your opponent casts a 2-cost spell, would you pitch your Mana Leak and this Shoal to counter? I guess not. If your opponent casts a 3-cost spell, would you pitch your Hinder (or Thoughtbind) and this Shoal to counter? You'll just cast one of the two. Blue should be the master of card advantage, and this card just doesn't help.
And I agree with the question on how will it stop "Tooth and Nail"?
With this card, you can reuse the effect of the Myojin's for casual play, but still not for tournament-caliber decks.