Wall of Shards

Defender, flying
Cumulative upkeep—An opponent gains 1 life. (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.)

The List

Coldsnap

Defender, flying
Cumulative upkeep—
An opponent gains 1 life. (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.)

When paying Wall of Shards’ cumulative upkeep, you may choose a different opponent for each age counter, or you can choose the same opponent multiple times.

Paying cumulative upkeep is always optional. If it’s not paid, the permanent with cumulative upkeep is sacrificed. Partial payments of the total cumulative upkeep cost can’t be made. For example, if a permanent with “cumulative upkeep {1}” has three age counters on it when its cumulative upkeep ability triggers, it gets another age counter and then its controller chooses to either pay {4} or sacrifice the permanent.