The Vulcano Dragon can be obtained through a tournement, the main prize for the dart game, and can be bought in the units page with cash, can possibly be bought for 50 cash by losing a battle on the mobile version (may result in a different dragon) and can be found in cash boxes. You can also transform into a Vulcano Dragon using a Rainbow Dragon.
The Vulcano Dragon
Has 4 attacks
1 - shoots fiery meteors at a single enemy
2 - rains down firey meteors on top of multiple enemies
3 - spins around quickly knocking enemies away
4 - can spawn Vulcano draggies (3 max)