Cheapest priced copy (Commander Masters): $0.39 at Card Kingdom, near mint, their price list as of .
Anafenza, Kin-Tree Spirit 
Legendary Creature — Spirit Soldier · 2/2 · Rare · Dragons of Tarkir · #2
Whenever another nontoken creature you control enters, bolster 1. (Choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
8 printings · $0.39 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 11 | Uncommon | $0.39 | $0.49 |
| Dominaria United Commander | 97 | Rare | $0.49 | — |
| Dragons of Tarkir | 2 | Rare | $0.49 | $0.79 |
| Multiverse Legends | 1 | Rare | $0.49 | $0.49 |
| Multiverse Legends | 66 | Rare | — | — |
| Multiverse Legends | 131 | Rare | — | $2.49 |
| Multiverse Legends | 131z | Rare | — | — |
| Dragons of Tarkir Promos | 2s | Rare | — | $0.69 |
2 rulings from Wizards of the Coast
- 25 February 2015You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves. That could be the creature with the bolster ability, if it's still under your control and has the least toughness.
- 25 February 2015Bolster 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 Aven Tactician's bolster ability.