Lumbering Falls — ruling 1

A land that becomes a creature may be affected by "summoning sickness." You can't attack with it or use any of its {T} abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature nor when it entered the battlefield.

Lumbering Falls — ruling 2

This land is colorless until the last ability gives it colors.

Lumbering Falls — ruling 3

When a land becomes a creature, that doesn't count as having a creature enter the battlefield. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters the battlefield won't trigger.

Lumbering Falls — ruling 4

An ability that turns a land into a creature also sets that creature's power and toughness. If the land was already a creature (for example, if it was the target of a spell with awaken), this will overwrite the previous effect that set its power and toughness. Effects that modify its power or toughness will continue to apply no matter when they started to take effect. The same is true for counters that change its power or toughness (such as +1/+1 counters) and effects that switch its power and toughness. For example, if Lumbering Falls has been made a 0/0 creature with three +1/+1 counters on it, activating its last ability will turn it into a 6/6 creature that's still a land.

Lumbering Falls : règles, fonctionnement et interactions (MTG)

Lumbering Falls is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

This land enters tapped. : Add or . : Until end of turn, this land becomes a 3/3 green and blue Elemental creature with hexproof. It's still a land.

How it works : Lumbering Falls

Original English text — Wizards of the Coast / Scryfall

#1August 25, 2015· Wizards of the Coast
A land that becomes a creature may be affected by "summoning sickness." You can't attack with it or use any of its abilities (including its mana abilities) unless it began your most recent turn on the battlefield under your control. Note that summoning sickness cares about when that permanent came under your control, not when it became a creature nor when it entered the battlefield.
No other card is named in this ruling.
#2August 25, 2015· Wizards of the Coast
This land is colorless until the last ability gives it colors.
No other card is named in this ruling.
#3August 25, 2015· Wizards of the Coast
When a land becomes a creature, that doesn't count as having a creature enter the battlefield. The permanent was already on the battlefield; it only changed its types. Abilities that trigger whenever a creature enters the battlefield won't trigger.
No other card is named in this ruling.
#4August 25, 2015· Wizards of the Coast
An ability that turns a land into a creature also sets that creature's power and toughness. If the land was already a creature (for example, if it was the target of a spell with awaken), this will overwrite the previous effect that set its power and toughness. Effects that modify its power or toughness will continue to apply no matter when they started to take effect. The same is true for counters that change its power or toughness (such as +1/+1 counters) and effects that switch its power and toughness. For example, if Lumbering Falls has been made a 0/0 creature with three +1/+1 counters on it, activating its last ability will turn it into a 6/6 creature that's still a land.
No other card is named in this ruling.