If damage would be dealt to you, put that many depletion counters on Force Bubble instead.
When there are four or more depletion counters on Force Bubble, sacrifice it.
At the beginning of each end step, remove all depletion counters from Force Bubble.
If you control more than one, each time you take damage you can decide which one replaces the damage, and that one replaces all of the damage. You can’t split the damage between them. You decide each time you take damage. Note that damage from multiple sources that happens at one time (such as combat damage) gives one choice, not one per source.