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 Cover of Winter. : Put an age counter on Cover of Winter.
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.
15-07-2006
wotc
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.
15-07-2006
wotc
If a creature has double strike, Cover of Winter prevents X of the combat damage it would deal during each combat damage step.
15-07-2006
wotc
Cover of Winter's replacement effect prevents combat damage creatures would deal to you and to attacking or blocking creatures you control.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.
(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. 
Wayne Reynolds2006-07-21
