Dreamcaller Siren — ruling 1

Dreamcaller Siren's last ability won't trigger if you don't control another Pirate as it enters the battlefield. If you lose control of each other Pirate before that ability resolves, it won't do anything.

Dreamcaller Siren : règles, fonctionnement et interactions (MTG)

Dreamcaller Siren 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

Flash Flying This creature can block only creatures with flying. When this creature enters, if you control another Pirate, tap up to two target nonland permanents.

How it works : Dreamcaller Siren

Original English text — Wizards of the Coast / Scryfall

#1September 29, 2017· Wizards of the Coast
Dreamcaller Siren's last ability won't trigger if you don't control another Pirate as it enters the battlefield. If you lose control of each other Pirate before that ability resolves, it won't do anything.
No other card is named in this ruling.