Winter's Rest — ruling 1

If the creature this Aura would enchant is an illegal target by the time Winter's Rest resolves, the entire spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.

Winter's Rest — ruling 2

If Winter's Rest is destroyed while its enters-the-battlefield triggered ability is on the stack, the creature that it enchanted is tapped as that ability resolves.

Winter's Rest — ruling 3

If you lose control of all of your other snow permanents, then control a new one, the effect of Winter's Rest will apply to the enchanted creature again.

Winter's Rest : règles, fonctionnement et interactions (MTG)

Winter's Rest 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

Enchant creature When this Aura enters, tap enchanted creature. As long as you control another snow permanent, enchanted creature doesn't untap during its controller's untap step.

How it works : Winter's Rest

Original English text — Wizards of the Coast / Scryfall

#1June 14, 2019· Wizards of the Coast
If the creature this Aura would enchant is an illegal target by the time Winter's Rest resolves, the entire spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.
No other card is named in this ruling.
#2June 14, 2019· Wizards of the Coast
If Winter's Rest is destroyed while its enters-the-battlefield triggered ability is on the stack, the creature that it enchanted is tapped as that ability resolves.
No other card is named in this ruling.
#3June 14, 2019· Wizards of the Coast
If you lose control of all of your other snow permanents, then control a new one, the effect of Winter's Rest will apply to the enchanted creature again.
No other card is named in this ruling.