Warning, it's undergone several revisions on beta so unsure what we'll see on live yet.

Abilities:

Halfus Wyrmbreaker

• Bind Will - Forces a dragon to obey his commands
• Dragon's Vengeance - Halfus takes 50% increased damage from all sources, stacks

Proto-Behemoth

• Fireball Barrage - Does 30K fire damage to enemies in an area

Notes:

• The fight centers around drakes giving abilities, and of the 5 drakes, 3 are active per week
• Random, so each week you'd have a new combination with new challenges to the fight
• You get a choice of which drakes to release, and subsequently kill.
• Each drake tends to give a raid wide debuff and or buff to Halfus
• When killed, they go away or lose some effectiveness or you gain some buff
• Also, when each are killed, they give Halfus stacking 50% damage taken debuff
• The Proto-Behemoth is just flying raid damage, not worth killing
• Constantly casts fireballs, spread out until you can kill the Time Warden (if up), after which you they slow down enough to see where they land to dodge
• Other than Drakes, tank and spank
• At 30%, he goes into constant whirlwind mode. Random target but tauntable for a while. Ranged burn asap. Slate Dragon stuns still apply to him.

The Drakes

Nether Scion

• Applies 100% attack speed buff to Halfus, gone when killed
• Gives raid-wide debuff reducing hit by 15%, attack speed by 15%, and damage by 25%, lasts till killed, applied on Halfus then (confirm?)

Time Warden

• When killed, slows down the speed of Proto-Behemoth's fireballs, allowing them to be dodged easily.   
• Heroic version roots everyone in place when controlled (maybe normal?)

Slate Dragon

• Gives Halfus, Malevolent Strikes - Reduces effectiveness of healing on target by 5%, stacks
• Furious Roar - Inflicts 10K physical damage to all enemies knocking them to the ground, 1.5 sec cast every 8-10 seconds, and should reduce damage taken by 100% for duration (confirm?)
• When stuns fades, Halfus recieves the stun and gets increased damage taken, for rest of the fight when killed

Orphaned Emerald Whelps

• Gives the Proto-Behemoth, Scorching Breath - Breaths flame in front of caster doing 9K fire damage
• Raid wide debuff reducing all damage done by 2000.

Storm Rider

• Raid wide debuff that interrupts spell casts every 0.5 seconds (use instants only).
• Gives Shadow Nova buff to Halfus, allows him to cast aoe knockback, 0.3 second cast, interruptable
• When killed, cast goes up to 4.5 second