In Tier 4, the boss fight is much more complex. There is also an additional reward for completing the entire instance within 35 minutes! Good luck, and good hunting!
I only did this once. But this is what I remember about the t4 boss fight.
You need to do a puzzle to get him to spawn. There are runes on the ground in a circle. Each rune has a symbol representing an animal. Each group member stands on a rune, but you have to get on them in the proper order - I believe it's the order of the encounters up until that point - but I'm not sure. I think if everyone steps on them all at the same time, it will also work.
So this spawns Kurnous.
As soon as Kurnous is agroed, everyone should grab a rabbit. They're hopping around. They will give you a run speed buff that will last the duration of the encounter.
Kurnous first attack is throwing lightning bolts at you. There will be a target ring on the ground where he is aiming for - RUN AWAY.
Around the ring of rune stones, there are portals. I think around 80% health, Kurnous will escape into one of these portals. You need to burn down the portal FAST. He'll keep trying to escape through others - so you have to watch for the portal opening - kill the portal.
Once that phase is done, he starts into the animals. I don't recall any special tricks other than keep moving, try and stay out of melee range if you not melee (stay behind) - basic tricks for dealing with mobs. He went down pretty easy once we got through the portal stage.
It was a fun encounter. I loved the trip on the giant eagles. I didn't win the roll on the cape. Once you had done the HV encounter once, you could by-pass the Vale and go right to the boss fight. But I never did this.
I also didn't get 5 Orders transformed into pigs dead - so didn't get the event title.