From the only reliable source of Catholic news on the net, Eye of the Tiber:
VATICAN–Pope Francis said in his morning Mass on Monday that if Martians came to him asking to be baptized he wouldn’t turn them away, but that when it came to krakens, unicorns, minotaurs, and British elves, he would have to say “absolutely not,” Vatican radio reports.
“If, for example, tomorrow an expedition of Martians came, and some of them came to us, here… Martians, right? Green, with that long nose and big ears, just like children paint them…and one says, ‘But I want to be baptized!’ What would happen?”
Pope Francis would not be one to turn away someone seeking baptism, even if they were an alien. He urged clergy to foster an open door policy for all to receive church teachings including Martians, but also urged them to not get carried away, and to immediately deny any golems, Chineese dragons, and even the Loch Ness Monstor.
Although the pope’s message was one of inclusion, saying “the Holy Spirit is not always predictable,” he justified his exclusion of other never seen creatures such as sirens and chupacabras by saying that he had to “draw the line somewhere.”
“Any entity, no matter how many tentacles it has, has a soul,” Consolmagno said in a talk preceding the British Science Festival in Birmingham. “But when it comes to creatures like Bigfoot, cyclopes, and hydras, His Holiness is absolutely correct.”
In response to a PopeWatch inquiry about Elvis Impersonators, the Vatican said that the Pope would reluctantly baptize them, but he absolutely refuses to do so for mimes.