Cheapest priced copy (Fate Reforged): $0.49 at Card Kingdom, near mint, their price list as of .
Sandsteppe Mastodon 
Creature — Elephant · 5/5 · Rare · Fate Reforged · #137
Reach
When this creature enters, bolster 5. (Choose a creature with the least toughness among creatures you control and put five +1/+1 counters on it.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fate Reforged | 137 | Rare | $0.49 | $0.49 |
| Fate Reforged Promos | 137 | Rare | — | $0.49 |
| Fate Reforged Promos | 137s | Rare | — | $0.49 |
2 rulings from Wizards of the Coast
- 24 November 2014You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves.
- 24 November 2014Bolster 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.