Dreamcaller Siren

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

Ixalan Promos

Ixalan

Flash
Flying
Dreamcaller Siren can block only creatures with flying.
When Dreamcaller Siren enters the battlefield, if you control another Pirate, tap up to two target nonland permanents.

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.