"All we have to do is open the doors and read the very first words in recorded history..."
—The Eleventh Doctor

Rootbound Crag

Rootbound Crag enters tapped unless you control a Mountain or a Forest.
{T}: Add {R} or {G}.

Bloomburrow Commander

Mutant strangler vines carried the town of Tanagra up into the treetops, where it remains to this day.

Fallout

Rootbound Crag enters the battlefield tapped unless you control a Mountain or a Forest.
{T}: Add {R} or {G}.

As this is entering, it checks for lands that are already on the battlefield. It won't see lands that are entering at the same time (due to Warp World, for example).

This checks for lands you control with the land type Mountain or Forest, not for lands named Mountain or Forest. The lands it checks for don't have to be basic lands. For example, if you control Temple Garden (a nonbasic land with the land types Forest and Plains), Rootbound Crag will enter untapped.