Chrono Lord Deja
This is a simple fight. This boss only has one major ability to watch out for, an Arcane Blast attack with a large range that hits your group for 1,000-2,000 arcane damage. During the entire fight spawns will still keep coming out of the portal and will need to be handled either by one or more members of your party or by summoning a Time Keeper (using Chrono-beacon) between the boss portal and Medivh, as the Keeper can easily take care of the adds and allows you to focus on the boss. Take care, however, as if you summon the Time Keeper too close to Chrono Lord Deja, the boss will immediately despawn it.
Temporus
Move the drake off to one the side of the gate where he spawns, so that he will not stand between Medivh and the Portal. This will prevent any of the small dragons accidentally aggroing on your group. If you still have a Chrono-beacon, you can spawn a Time Keeper on the path of the small dragons to keep them away from Medivh for some time, but do not spawn your Keeper too close to the boss or else he will instantly despawn it. As long as Temporus is not hastened, your tank may be able to run out of the Mortal Wound debuff range once it stacks too high for healing to be effective. Make sure your tank does not move too far from the portal when waiting or Temporus will reset. Due to the stacking nature of his debuff, you may use another player to temporarily pull aggro from the main tank to allow the debuff to expire. However, it is important to note that this boss is not tauntable.
It is extremely important to remove his Hasten effect when it appears as it can quickly speed up how often the Mortal Wound debuff is applied. A mage's Spellsteal is ideal for removal, though Purge, Dispel Magic, etc. work as well. Detect Magic cast early will help, otherwise, be on the lookout for white rings to appear around his feet as an indicator that his
Hasten buff is up.
Aeonus
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Tranquilizing Shot will remove Aeonus's frenzy. Hunters need to be aware of this, as it can significantly reduce the massive DPS that Aeonus can dish out.
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Spell Reflection can be used to negate the effect of Time Stop, and give the tank time to use cooldowns such as potions or Shield Wall if need be.
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Wiping on this boss doesn't necessarily mean the end of the instance as it would if it happened on any other portal. Aeonus does not spawn any non-elite dragonkin, and he does not deplete Medivh's shield any faster than the other dragons. If Medivh's shield is high enough to withstand around 50-65% damage, the whole group will have time to run back and begin the fight again.