Health:

• Heroic:  24M
• Normal:  6.9M

Abilities:

• Flame Jets:  Stomps the ground causing geysers of flame to errupt under all enemies. These geysers deal 8483 to 9517 Fire damage, knocking the targets into the air and interrupting any spells being cast for 8 sec. In addition, the targets take 2000 Fire damage per second for 8 sec. 2.7 sec cast
• Scorch:  Fires a jet of flame, burning all enemies in front of the caster within 30 yards, dealing 3770 to 4230 Fire damage every half-second for 3 sec. Additionally, the ground is scorched by this effect causing it to catch on fire, dealing 7540 to 8460 Fire damage every second to all enemies within 13 yards. Iron Constructs within this radius will begin to heat up, eventually becoming molten.
• Slag Pot:  Charges and grabs a random enemy target, tossing them into the caster's slag pot. The target is unable to attack the caster and takes 7500 Fire damage every second for 10 sec. If the target survives, they are imbued with the magical slag, increasing their haste by 150% for until cancelled.
• Strength of the Creator:  Increases Ignis' damage by 15% each time an Iron Construct spawns. Stacks up to 99 times.

Iron Contructs:

• Heat:  Blasts all nearby Iron Constructs with intense heat, increasing their movement speed by 5% and haste by 5%. This effect stacks up to 20 times. If this effect stacks to 20, the affected Iron Construct will become Molten
• Molten:  The Iron Construct becomes Molten, increasing haste by 100%. In addition, Flames errupt out from the caster every second, dealing 4713 to 5287 Fire damage to enemies within 7 yards. Drag the Construct in the water and it will become Brittle.
• Brittle:  The cold water causes molten Iron Constructs to rapidly solidify, rendering them unable to act. In addition, if they are dealt more than 5000 damage during this state, they will shatter, dealing 18850 to 21150 damage to all enemies in a 10 yard radius.
• Shatter:  Deals 18850 to 21150 Physical damage to all enemies within 10 yards. Damage from this effect ignores armor.

The Fight:

This is mostly a tank and spank fight, but can hit the tank hard, upwards of 30K.   He will occasionally scorch the ground in front of him, so just move away.

Casters need to pay attention to Flame Jets timer, when it goes off it'll interrupt any spell casting for 8 seconds.   They are spells that are resistable or whatever spell avoidance immunity you got.   So use em to help mitigate damage.

Randomly charges and throws someone in the slag pot dealing 5000 damage per second, so heal him.  Should he live, he'll get a haste buff.    You can cast in it still, and use spells that make you immune, however if you do anything to remove the debuff, you will not get the buff afterwards (haste), and will not get the personal achievement.

There are constructs in the room he'll activate.   Each one active increases his damage by 15%, off tank em.

The way to kill those is to drag em into the scorched ground til they become Molten (stack to 20), then drag them to the pools of water.   They'll be rendered unable to act for 15 sec, so run away and ranged blow em up, a single 5K hit will kill it.   Not collective damage, a single hit.

We settled on more of a 3 point drop off locations for the scorch.   Left, Center, Right sides of the pool of water, both sides, and dropping it about 3 times between each pool on either side.   This keeps the scorches relatively close so the OTs can drag Constructs into them before they wear off.   The raid mostly stands in the middle, with only some healers and DPS to move in range for shattering Constructs.

The Trash:

There's a pair of fire giants, and a few pairs of golems, and pairs of elementals.    Here's the quick and dirty versions...

Fire Giants:  Tank em apart, they do a damaging fire aura to everyone in range.    Even after death so stay away from their corpses.

Golems:  Charged people and put a slowing attack speed debuff on tank.  Nothing huge.

Elementals:  These have a trick we remember.   They spawn out 2 fire cyclones that knock you around and do I believe 7K damage per tick.    Run away run away.   Melee could run away, but I kind of found when they spawn, they aren't really that lethal, they knock you way back.    So as long as the cyclones aren't chasing you down in particular to get hit again, just run back.

Achievements:

Shattered:  Defeat Ignis the Furnace Master after shattering 2 Iron Constructs within 5 seconds on Normal/Heroic Difficulty.

This does not require you to kill Ignis within that timeframe either.  It's only asking you to shatter 2 within 5 seconds.   Then don't wipe.     So easiest thing is to gather 2, drag em to fire, then blow em up.  Then continue the rest of the fight normally.

Hot Pocket:  Survive being thrown into Ignis the Furnace Master's Slag Pot on Normal/Heroic Difficulty

This would be a personal achievement.  Part luck to be chosen, part healers to heal you through it.   Do not use bubbles (or equivalent) to escape it if you want this achievement.

Stokin' the Furnace:  Defeat Ignis the Furnace Master in 4 minutes on Normal/Heroic Difficulty

Just a straight dps it down in time thing.   Quite easy once this fight is on farm, don't really even need special stacking if you got decent dps.

Sources:

• http://www.wowwiki.com/Ignis_the_Furnace_Master
• http://www.stratfu.com/strats/Ignis
• http://www.mmo-champion.com/index.php?page=839