Sulfuron Harbinger

#1. Before the fight:

This fight is one of the longer fights in Molten Core, so you can make make great use of a pet toy here, such as [Ancient Cornerstone Grimoire] or [Arcanite Dragonling] or [Mithril Mechanical Dragonling], etc.
(Do NOT use [Gnomish Battle Chicken] as it is bugged in WoW: Classic.)

#2. During the fight:

Use [Free Action Potion] after Sulfuron's adds are killed. It will nullify Sulfuron's Hand of Ragnaros.
This boss comes with friends. Make sure your AoE is available and off cooldown.
Combine Adrenaline Rush and Blade Flurry for maximum DPS.
[Goblin Sapper Charge] off the bat might get you killed, so keep your [Limited Invulnerability Potion], Evasion and Vanish handy.