Vistrix :
I think Vixstrix is one of the most encounters in AoC. Once the aggro is fixed it should be fine.
Champion of the Honourguard :
It's just your average zerg encounter really. Lacks any real scripting and tactics apart from "Stop DPS".
Kylikki :
Fun but the wolves which spawn need to add something more to the encounter. All they currently do is remove two from the boss as they kite around room. Add some type of script like attacking a random healer etc.
Yakmar:
A giant slug who pops more giant slugs. Ugliest boss I've seen

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Tier 2:
Gargoyle Master:
The 15 minute stun is just to long and ends up with people just sitting around while it wears off. Maybe make GM stun a bit a more but a lower timer, something like 30 seconds or so. As there is no real curing for healers then 15 mins is just to long imo.
Ahazu Zagam: Another really fun enounter. Just fixing the reset bug should be enough. Apart from I thinks it fine as is.