Abandoned Hall

Our first battlefield with a triggered ability anyone can trigger that targets game objects was printed in Unleashed and it has unearthed some strangeness in the battlefield control rules. That battlefield is Abandoned Hall.

190.6.c. If an Ability of a Battlefield indicates that a specific player makes a choice, that player is the Ability's controller. They take responsibility for adding it to the chain if applicable and make all choices required by the ability. They and only they control the ability, regardless of who controls the Battlefield. Example: Abandoned Hall is a battlefield that reads "When a player plays a spell, they may give a unit they control here +1 might this turn." The ability indicates that the player who played the spell makes the choice, so that player takes responsibility for putting the ability on the chain and makes all choices. They control the triggered ability.

506.3.e.10. A trigger would require a player to choose something, such as a unit or gear, even if there is only one legal choice. (Example: Abandoned Hall)