Green fire is The Codex of Xerrath, a passive warlock ability that recolors the class's fire spells fel-green. It is earned by beating Kanrethad Ebonlocke at the end of Pursuing the Black Harvest, a warlock-only solo scenario set in a private version of the Black Temple. Blizzard shipped it in patch 5.2.0 on March 5, 2013 and it is still obtainable on current retail.
Where it starts: the Sealed Tome of the Lost Legion, which only a warlock can loot. It drops off mobs on the Isle of Thunder in Pandaria, with a better chance off that zone's rare spawns. Blizzard has never published a rate for it, so the tome is a pure RNG roll — but it is tradeable, so it can also be bought outright on the auction house. Fusing it with a Healthstone creates the Codex and starts the quest.
The chain is six quests — An Unusual Tome, Reader for the Dead Tongue, A Tale of Six Masters, Seeking the Soulstones, Seek the Signal, Infiltrating the Black Temple — plus the optional Plunder the Black Temple. Seeking the Soulstones alone sends you to four Outland zones. Everything is flagged level 35 after the level squish, but the scenario's nine stages and the Kanrethad fight are only comfortable at max level, where a modern warlock heavily out-scales the original level-90 tuning.
It is not account-wide. The Codex is learned by one warlock and every alt has to run the whole thing again. There is no lockout and no respawn window to wait on. The Breaker of the Black Harvest feat and the "of the Black Harvest" title were retired at the launch of Warlords of Draenor, so the fel-green spell effect is the reward that remains — and it toggles on and off for free at the Altar of Damnation in Shadowmoon Valley.
Realistic time: about 3 to 4 hours with the tome already in your bags, which is the $53.99 block. Tome farming is open-ended, so it is booked as repeat blocks at the same hourly rate rather than a bigger tier. Pick US or EU, then hours: 2, 4, 6 or 10 at $26.99, $53.99, $80.99 or $134.99. Piloted is the default, Self-play Remote is +30%, Express +20%, Super Express +40%. Manual play only on timesaver.gg, scheduled in ET or PT.
