A Sintillian is a race of alien, introduced in Men in Black: The Series. They are reptilian/dinosaur and vaguely human-like in their appearance. Sintillians walk on two legs, and wear clothes like humans, but they do have a long tail. They also have a long mouth, ten eyebrows, and a long tail on the back of their heads.
Most of what they can do is unknown, but it is shown that they can open up their chests to show organs.
In The Alpha Syndrome, a Sintillian comes to MiB with a problem. He shows Jay that he has lost his heart. He reveals that it was stolen right from his body. After long investigating, Jay and Kay find the culprit is Alpha, a former MiB agent, who left Kay for dead long ago. Alpha shoots the Sintillian Heart, but they are able to save the heart and the Sintillian.