We felt that these two cards along with Bolas would give the set just a touch of Bolas's colors
I might cast a spell to kill your knight, but another player might counter that spell, nullifying it for their own gain
Crew 1 makes it very easy to have at least a few of them active each turn, and you only actually have to sacrifice three permanents to turn the entire fleet into flying creatures
As a result, it is harder to ignore Valakut decks and just race
Myr Battlesphere - Another popular ramp finisher, this is a great one to flicker because it not only swarms, but can use that swarm by attacking with itself for big damage and then get flickered again after the ability resolves before dying to a lethal block
Wizards also took the opportunity to clean up the mechanic a bit (Sneak counts as casting, unlike Ninjutsu)