To protect the alliance between Kjeldor and Yavimaya, they trained in the ways of both.

Juniper Order Ranger

Whenever another creature you control enters, put a +1/+1 counter on that creature and a +1/+1 counter on Juniper Order Ranger.

March of the Machine Commander

Whenever another creature enters the battlefield under your control, put a +1/+1 counter on that creature and a +1/+1 counter on Juniper Order Ranger.

Midnight Hunt Commander

The List

Commander Anthology Volume II

Commander 2016

The creature doesn't enter with a +1/+1 counter on it. It enters, then the ability triggers. If either that creature or Juniper Order Ranger leaves the battlefield before the ability resolves, the remaining creature will still get a +1/+1 counter.