Oran-Rief, the Vastwood

Land

This land enters tapped.

: Add .

: Put a +1/+1 counter on each green creature that entered this turn.

Oran-Rief's last ability cares about permanents' characteristics at the time the ability resolves, not their characteristics at the time they entered. For example, if a blue creature enters, then is turned green by a spell or ability, then Oran-Rief's second ability resolves, you'll put a +1/+1 counter on that creature.
Oran-Rief's last ability affects all permanents that are green creatures that entered this turn, not just the ones you control.