Map the Wastes — ruling 1

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.

Map the Wastes — ruling 2

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

Map the Wastes : règles, fonctionnement et interactions (MTG)

Map the Wastes is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Bolster 1. (Choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

How it works : Map the Wastes

Original English text — Wizards of the Coast / Scryfall

#1November 24, 2014· Wizards of the Coast
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.
No other card is named in this ruling.
#2November 24, 2014· Wizards of the Coast
You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves.
No other card is named in this ruling.