From the Super Mario Wiki
Leaping Flames are fiery, serpent-like monsters from Donkey Kong Country Returns and Donkey Kong Country Returns 3D. They appear after the fireball bombard in Hot Rocket, a level in the Volcano world.
As they emerge from lava, Leaping Flames begin chasing the Rocket Barrel-riding Kongs by revolving around them on a short distance. This way, the enemies attempt to cage the Kongs and limit their movement. If the characters crash their vehicle into a Leaping Flame, they will destroy it and lose a life. Leaping Flames cannot be destroyed, and as they crowd around the Kongs, they become more difficult to avoid. After attempting to attack, they move behind the Kongs.