Drana's Chosen
Creature — Vampire Shaman Ally
Cohort — 
, Tap an untapped Ally you control: Create a tapped 2/2 black Zombie creature token.
"Drana commands me. I command my nulls. And so her bidding is done."
Deruchenko Alexander
Rulings
To activate a cohort ability, the Ally with that ability must have been under your control continuously since the beginning of your most recent turn. Informally, it can’t have “summoning sickness.” However, the other Ally you tap can be one that just came under your control. (Note that tapping the second Ally doesn’t use {T} [the tap symbol].)
(wotc • 2016-01-22)
Rulings
To activate a cohort ability, the Ally with that ability must have been under your control continuously since the beginning of your most recent turn. Informally, it can’t have “summoning sickness.” However, the other Ally you tap can be one that just came under your control. (Note that tapping the second Ally doesn’t use {T} [the tap symbol].)
(wotc • 2016-01-22)