There are 10 bosses in the Molten Core raid. The raid is a volcanic stronghold beneath Blackrock Mountain, where players confront powerful elemental and fire-themed servants of Ragnaros, the Firelord.
Molten Core was one of World of Warcraft’s original level-60 raids and was designed for large groups of up to 40 players. Its encounters include the elemental giant Lucifron, the core hounds Magmadar and Gehennas, the lava lord Geddon, and the ancient dragonkin Razorgore—wait, Razorgore belongs to Blackwing Lair, not Molten Core. Molten Core’s actual later bosses include Garr, Shazzrah, Sulfuron Harbinger, Golemagg the Incinerator, Majordomo Executus, and finally Ragnaros.
A common mix-up is counting only the major named encounters or confusing Molten Core with Blackwing Lair, which has a different boss roster. Ragnaros is the raid’s climactic encounter, but he is one of the 10 bosses rather than an additional boss beyond the listed total.