When this creature enters, you may sacrifice another creature or enchantment. When you do, this creature deals 2 damage to any target.
You don't choose a target for Boilerbilges Ripper's ability at the time it triggers. Rather, a second "reflexive" ability triggers when you sacrifice another creature or enchantment this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.