linvala also needs protection from white, blue and green.... white can exile her, blue can bounce her and green can kill her because she flies. there are more threats to one single creature than just black and red....
Ward sliver is a staple in every sliver deck since it first came out....
Mana Crypt..... i have seen high dollar tournaments both won and lost by this card.... a very risky card but when it does pay off, it is well received.