Loyal Pegasus

• WWizards of the Coast2019-07-12
  Official Ruling
  In a Two-Headed Giant game, Loyal Pegasus can attack or block with a creature controlled by your teammate, even if no other creatures you control are attacking or blocking.
• WWizards of the Coast2019-07-12
  Official Ruling
  If you control more than one Loyal Pegasus, they can attack or block together, even if no other creatures attack or block.
• WWizards of the Coast2019-07-12
  Official Ruling
  If an effect says that Loyal Pegasus attacks or blocks "if able," and you control one or more other creatures that are able to attack or block, you must attack or block with Loyal Pegasus and at least one other creature.
• WWizards of the Coast2019-07-12
  Official Ruling
  Although Loyal Pegasus can't attack alone, other attacking creatures don't have to attack the same player or planeswalker. For example, Loyal Pegasus could attack an opponent and another creature could attack a planeswalker that opponent controls. Similarly, other blocking creatures don't have to block the same creature that Loyal Pegasus blocks.
• WWizards of the Coast2019-07-12
  Official Ruling
  Once Loyal Pegasus has attacked or blocked, it will remain in combat even if you no longer control another attacking or blocking creature.

Rulings via Scryfall