Cover of Winter — ruling 1

Cover of Winter's replacement effect prevents combat damage creatures would deal to you and to attacking or blocking creatures you control.

Cover of Winter — ruling 2

If multiple creatures would deal combat damage to you and your creatures at the same time, this prevents X of the damage that would be dealt by each of them. This prevention is applied creature by creature. For example, if Cover of Winter has two age counters and you're being attacked by an unblocked 1/1 and an unblocked 4/4, this will prevent 2 of the combat damage that would be dealt by each one. All damage from the 1/1 is prevented and 2 damage from the 4/4 is prevented, meaning you're dealt 2 damage.

Cover of Winter — ruling 3

If a creature has double strike, Cover of Winter prevents X of the combat damage it would deal during each combat damage step.

Cover of Winter — ruling 4

If a creature's combat damage is assigned to multiple recipients (for example, if it has trample and is blocked by two creatures, and damage is assigned to each of those creatures and to you), you decide how to divide the prevention effect. You may prevent damage that would be dealt to the first creature, the second creature, and/or you, as long as the total amount of that creature's damage that would be prevented is X.

Cover of Winter : règles, fonctionnement et interactions (MTG)

Cover of Winter 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

Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it. can be paid with one mana from a snow source.) If a creature would deal combat damage to you and/or one or more creatures you control, prevent X of that damage, where X is the number of age counters on this enchantment. : Put an age counter on this enchantment.

How it works : Cover of Winter

Original English text — Wizards of the Coast / Scryfall

#1July 15, 2006· Wizards of the Coast
Cover of Winter's replacement effect prevents combat damage creatures would deal to you and to attacking or blocking creatures you control.
No other card is named in this ruling.
#2July 15, 2006· Wizards of the Coast
If multiple creatures would deal combat damage to you and your creatures at the same time, this prevents X of the damage that would be dealt by each of them. This prevention is applied creature by creature. For example, if Cover of Winter has two age counters and you're being attacked by an unblocked 1/1 and an unblocked 4/4, this will prevent 2 of the combat damage that would be dealt by each one. All damage from the 1/1 is prevented and 2 damage from the 4/4 is prevented, meaning you're dealt 2 damage.
No other card is named in this ruling.
#3July 15, 2006· Wizards of the Coast
If a creature has double strike, Cover of Winter prevents X of the combat damage it would deal during each combat damage step.
No other card is named in this ruling.
#4July 15, 2006· Wizards of the Coast
If a creature's combat damage is assigned to multiple recipients (for example, if it has trample and is blocked by two creatures, and damage is assigned to each of those creatures and to you), you decide how to divide the prevention effect. You may prevent damage that would be dealt to the first creature, the second creature, and/or you, as long as the total amount of that creature's damage that would be prevented is X.
No other card is named in this ruling.