Bloodline Pretender

• WWizards of the Coast2021-02-05
  Official Ruling
  If an effect causes a creature with changeling to lose all abilities, it will remain all creature types, even though it will no longer have changeling. This is because changeling applies before the effect that removes it.
• WWizards of the Coast2021-02-05
  Official Ruling
  Changeling is a characteristic-defining ability. It functions in all zones, not only while a card that has it is on the battlefield.
• WWizards of the Coast2021-02-05
  Official Ruling
  The subtype Shapeshifter that appears on the type line is mostly there to reinforce the flavor. A creature card with changeling is just as much an Elf, a Dwarf, a Sliver, a Goat, a Coward, and a Zombie as it is a Shapeshifter.
• WWizards of the Coast2021-02-05
  Official Ruling
  You must choose an existing creature type, such as Vampire or Druid. You can't choose card types (e.g., artifact) or supertypes (e.g., snow).
• WWizards of the Coast2021-02-05
  Official Ruling
  If Bloodline Pretender enters the battlefield at the same time as another creature, you can choose one of that creature's creature types and have Bloodline Pretender's last ability trigger for that other creature.
• WWizards of the Coast2021-02-05
  Official Ruling
  If Bloodline Pretender is somehow on the battlefield without a chosen creature type, its last ability can't trigger, even if a creature with no creature types enters the battlefield.
• WWizards of the Coast2021-02-05
  Official Ruling
  If an effect causes a creature with changeling to become a new creature type, it will be only that new creature type. It will still have changeling; the effect making it all creature types will simply be overwritten.

Rulings via Scryfall