Astrid, Faithless Master

As long as you control 3 or more assassins, Astrid, Faithless Master gets +2/+0 and has Menace
Sacrifice a creature: Permanents you control gain indestructible until end of turn.
{2}{p/b}{t} Put an assassin from your hand onto the battlefield.
"The Night Mother represents a chapter in the Dark Brotherhood's history that has long since been closed.
Today we live by our own rules."