Enchantment, W (1) At the beginning of your upkeep, you may put a verse counter on Serra's Hymn. Sacrifice Serra's Hymn: Prevent up to X damage total that would be dealt this turn to any number of target creatures and/or players, divided as you choose, where X is the number of verse counters on Serra's Hymn.1
Illus. Rebecca Guay
You count the number of counters, then divide up the prevention during the announcement of the ability. Each targeted creature receives the appropriate amount of damage prevention when the ability resolves. [D'Angelo 2003/02/16]
Adding a counter is optional. If you forget to add one during your upkeep, you cannot back up and add one later. [Urza's Saga Rule Page]
You can play the ability (choosing no targets) even if there are no verse counters on it. It doesn't do anything useful if you do this. [D'Angelo 2003/05/19]
If there is at least one verse counter on this, you cannot choose zero targets. You must choose between 1 and X targets. [DeLaney 2003/05/19]