Ursa

Ursas are magical gigantic bears which have fur that look like the night sky. The two known "kinds", Ursa Minor and Ursa Major, are named after the star constellations in the northern sky, also known as the Little Bear and Great Bear, or Little Dipper and Big Dipper. Both Ursas made an appearance in the episode Boast Busters.

Ursa Minor
An Ursa Minor is a large, blue bear with fur that matches the night sky and has white stars on its body, and a large star on its forehead. It is later revealed to be an infant to the Ursa Major. In Boast Busters, a couple of male ponies, Snips and Snails, decide to venture into the forest to find an Ursa Major, so they'd be able to see Trixie face off against it. They stumble upon a giant magical bear, believing it's an Ursa Major. The bear chases them to Ponyville and proceeds to wreak havoc, destroying a few buildings and crushing Trixie's trailer. Trixie admits she cannot vanquish the beast, prompting Twilight Sparkle to soothe it with music, and feed it with an improvised giant milk bottle. Once the monster's asleep, she uses magic to float it back to its cave, into its mother's arms.

Ursa Major
An Ursa Major is a giant magical purple bear, and the parent of an Ursa Minor. Ursa Majors are mentioned several times in the episode Boast Busters, when Trixie claimed to have vanquished one. Later, when Ponyville is under attack by a giant bear believed to be an Ursa Major, Trixie confesses that she cannot defeat it and never had vanquished an Ursa Major. An actual Ursa Major makes an appearance in the end of the episode, cradling the Ursa Minor that has just been returned to it.