Ancient Core Hound
These ferocious dogs have a frontal bite AoE and a random effect AoE. Furthermore, they use a frontal fire AoE which is quite devasting if hitting the entire raid-group. Have the main tank keep the Hound turned away while everyone else attacks from the back. Some AoEs may make the fight more annoying, but keeping aggro is all this is required. Ancient Core Hounds stop respawning after Magmadar has been killed. However, before you manage to kill Magmadar, those beasts respawn in approximately 18 minutes and timing the respawn is absolutely crucial to any raid new to the Molten Core.
Note: If you kill Magmadar and any Ancient Core Hounds still live, when you return the next day, they will have despawned. The exact despawn timer is unknown.