Steal a creature in response?

[Taysby]

So I have out {Rubina soul singer} and my opponent has out {shatter gang brothers}. He activates his ability to make me sacrifice an enchantment.  In response, I take it with my soul singer.  Do I still have to sac an enchantment, or does it make all of MY opponents sac something because I control him now and so it'd be my opponents.

[Pleeb]

Once your opponent activates the ability, it's his. You can gain control of his creature, but once the sac ability resolves, you'll have to sac an enchantment.

To use a beaten down metaphor: once the arrow is released, it doesn't matter what happens to the archer.

[abstractApathist]

I think I figured out why, when you activate it, you choose all targets for it first, and then people are allowed to respond.  I thought that it might choose the targets upon resolution because it doesn't say choose or target.

If it doesn't say target, then there aren't any targets. When you steal {Shattergang Brothers}, you don't steal his already activated ability. There are no spells that let you take control of an ability, even if you steal the ability's source.

[abstractApathist]

However, when the ability resolved, would it see who the opponents are for the controller of shatter gang?  If the opponents don't get chosen upon casting it, it happens when it resolves, and would it see the brothers current or old opponents?

No. The activates ability is not tied to its source, but the player that activated it.

109.5.: The words "you" and "your" on an object refer to the object's controller, its would-be controller (if a player is attempting to play, cast, or activate it), or its owner (if it has no controller). For a static ability, this is the current controller of the object it's on. For an activated ability, this is the player who activated the ability. For a triggered ability, this is the controller of the object when the ability triggered, unless it's a delayed triggered ability. To determine the controller of a delayed triggered ability, see rules 603.7d-f.

RESOLVED

[abstractApathist]

As illustrated, once the ability is on the stack, it will continue to recognize the player who activated it (or controlled the source of the triggered ability at the time it triggered) as its controller. This point of reference is used when dealing with terms like "opponent" and "other players." Unless the ability is countered, it will be very difficult to avoid effects like this.

And thank you for the rules citation, Abstract. Always helpful.

No problem! Glad to be helpful.