Yuuzhan Vong ( Grysk )

The Grysk species, introduced in Timothy Zahn's sequel trilogy novel Thrawn: Alliances, is a highly aggressive and extra-galactic entity. They are a warrior-based nomadic species and are known for their slave-taking and manipulative behavior. They originated from the Unknown Regions and were a significant threat to the Chiss Ascendancy, the native people of Grand Admiral Thrawn. Despite living far from Star Wars’ usual settings, they had a significant impact on its universe. They primarily communicate through a quantum-entangled communication method and possessed advanced technology.

One of their unique strategies was their ability to manipulate other species to wage war on their behalf. The Sith Lord Darth Sidious (Emperor Palpatine) viewed the Grysk as a significant threat to his future Empire. He followed Thrawn's advice and kept a watchful eye on this alien species. They are seen as a mystery, with unknown social structure, numbers or home base, making them a fascinating part of the Star Wars lore.

On the other hand, the Yuuzhan Vong are a technophobic, fanatical, and pain-worshipping species in the Star Wars expanded universe. They originated from the non-canon novel series Star Wars: The New Jedi Order by Del Rey. Just like the Grysk, the Yuuzhan Vong are leaders in an extra-galactic invasion, and fought against the protagonists of the Star Wars galaxy for five years, known as the Yuuzhan Vong War.

The Yuuzhan Vong are extremely durable and have a unique connection to their bio-engineered tech and weaponry. Unlike any other species in Star Wars universe, they are invisible to The Force. This characteristic made them a significant problem to tackle by the Jedi and provided an interesting direction in the novel series to explore The Force's nature.

Interestingly, there has been speculation among fans and authors alike that the Grysk were introduced as a replacement for the non-canon Yuuzhan Vong, with several notable similarities between the two. However, this has not been officially confirmed by the creators of the Star Wars franchise. Regardless, both species present a fascinating glimpse into the potential threats that exist outside the known Star Wars galaxy, keeping fans on their toes for potential future stories.