Ruins of Oran-Rief

Ruins of Oran-Rief enters tapped.
{T}: Add {C}. ({C} represents colorless mana.)
{T}: Put a +1/+1 counter on target colorless creature that entered this turn.

Modern Horizons 3 Commander

Ruins of Oran-Rief enters the battlefield tapped.
{T}: Add {C}.
{T}: Put a +1/+1 counter on target colorless creature that entered the battlefield this turn.

Commander Masters

Oath of the Gatewatch Promos

Oath of the Gatewatch

Ruins of Oran-Rief enters the battlefield tapped.
{T}: Add {C} to your mana pool. ({C} represents colorless mana.)
{T}: Put a +1/+1 counter on target colorless creature that entered the battlefield this turn.

The target of the last ability didn’t necessarily have to be a colorless creature as it entered the battlefield, provided it entered the battlefield during that turn. However, it does have to be a colorless creature to be a legal target of the ability.