Grovetender Druids
Creature — Elf Druid Ally
Rally — Whenever this creature or another Ally you control enters, you may pay 
. If you do, create a 1/1 green Plant creature token.
"The seedlings scream for us to loose them upon the Eldrazi, and we shall oblige."
Chase Stone
Battle for Zendikar (BFZ)
• #212Rulings
If a creature with a rally ability enters the battlefield under your control at the same time as other Allies, that ability will trigger once for each of those creatures and once for the creature with the ability itself.
(wotc • 2015-08-25)
When an Ally enters the battlefield under your control, each rally ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve.
(wotc • 2015-08-25)
Rulings
If a creature with a rally ability enters the battlefield under your control at the same time as other Allies, that ability will trigger once for each of those creatures and once for the creature with the ability itself.
(wotc • 2015-08-25)
When an Ally enters the battlefield under your control, each rally ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve.
(wotc • 2015-08-25)