Blood Thirst Feral

All Vampires you control gain Frenzy 2 and
Shadow.
Frenzy 2 (Whenever this creature attacks and isn't
blocked, it gets +2/+0 until end of turn.)
Shadow (This creature can block or be blocked by
only creatures with shadow.)
Any player may sacrifice a creature to Blood
Thirst Feral before combat to Silence it until
end of turn.