2014-11-24

You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves.

2014-11-24

Count the number of tapped creatures you control as the ability resolves to determine the value of X.

2014-11-24

Bolster itself doesn't target any creature, though some spells and abilities that bolster may have other effects that target creatures. For example, you could put counters on a creature with protection from white with Abzan Skycaptain's bolster ability.

2014-11-24

The creature you put the counters on doesn't have to be one of the tapped creatures.