A mastodon's path always leads to an oasis.

Sandsteppe Mastodon

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.)

Magic Online Promos

Fate Reforged

Reach
When Sandsteppe Mastodon enters the battlefield, bolster 5. (Choose a creature with the least toughness among creatures you control and put five +1/+1 counters on it.)

Fate Reforged Promos

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.

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