Cliffrunner Behemoth — ruling 1

As long as at least one permanent you control is the specified color, the ability will "work" and grant this creature the bonus. Otherwise, it won't have the bonus.

Cliffrunner Behemoth — ruling 2

Whether Cliffrunner Behemoth has haste matters only when attackers are declared. Once it's been declared as an attacker, it doesn't matter if it loses haste.

Cliffrunner Behemoth — ruling 3

Whether Cliffrunner Behemoth has lifelink matters only when it deals damage (that is, at the point when its combat damage resolves, or at the point when a spell or ability that causes it to deal damage resolves). For example, if your only white permanent is a creature that receives lethal damage at the same time Cliffrunner Behemoth deals damage, the lifelink ability will still apply and you'll gain life.

Cliffrunner Behemoth : règles, fonctionnement et interactions (MTG)

Cliffrunner Behemoth 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 creature has haste as long as you control a red permanent. This creature has lifelink as long as you control a white permanent.

How it works : Cliffrunner Behemoth

Original English text — Wizards of the Coast / Scryfall

#1February 1, 2009· Wizards of the Coast
As long as at least one permanent you control is the specified color, the ability will "work" and grant this creature the bonus. Otherwise, it won't have the bonus.
No other card is named in this ruling.
#2February 1, 2009· Wizards of the Coast
Whether Cliffrunner Behemoth has haste matters only when attackers are declared. Once it's been declared as an attacker, it doesn't matter if it loses haste.
No other card is named in this ruling.
#3February 1, 2009· Wizards of the Coast
Whether Cliffrunner Behemoth has lifelink matters only when it deals damage (that is, at the point when its combat damage resolves, or at the point when a spell or ability that causes it to deal damage resolves). For example, if your only white permanent is a creature that receives lethal damage at the same time Cliffrunner Behemoth deals damage, the lifelink ability will still apply and you'll gain life.
No other card is named in this ruling.