Whip Vine 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

Defender; reach (This creature can block creatures with flying.) You may choose not to untap this creature during your untap step. : Tap target creature with flying blocked by this creature. That creature doesn't untap during its controller's untap step for as long as this creature remains tapped.