It is rather on the all in side, not only because it hits your total resources pretty hard but because of the style of deck where Smallpox is optimal - if all your cards are cheap (or at least the ones you plan to cast) then you are less likely to have that much late game legs
So here we get to potentially double up counters on something twice if we give Bright-Palm haste and the counter to another creature, and some evasion against chump blockers
In addition to having flash, when Evelyn or another vampire enters the battlefield, you get to exile the top card of every player's library and set it aside to cast later, using any color of mana to do so
If someone swept your board, you can get back your death triggers (Zulaport Cutthroat), sacrifice engines (Viscera Seer) and fodder after a mass removal spell would have otherwise stopped you
And possibly viable
We were returning to New Phyrexia, formerly Mirrodin, the only plane where the Myrs exist, so we knew we wanted some new ones
