Dominaria Spoiler Digest - Who's Who and What's What from the Release Notes
Devour 1 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with that many +1/+1 counters on it.)
Each other creature you control enters the battlefield with an additional X +1/+1 counters on it, where X is the number of +1/+1 counters on Bloodspore Thrinax.
11/4/2015 If Bloodspore Thrinax enters the battlefield at the same time as other creatures you control, those creatures won’t get additional +1/+1 counters from Bloodspore Thrinax’s last ability. Those creatures also can’t be devoured by Bloodspore Thrinax.