I went to Herd Mode with 5 ppl after we got all achievements except for the 3 named including x2 one. But although we hailed to Estir, it didn't get into the waiting time to pop the other one up. Do we need 6 ppl?
I had the same thing in the solo zone. I hailed Estir and she immediately became aggro. As it was the first time I'd done it I wasn't sure if you had to have run it previously to be able to get the others or if I had done something wrong early on.
Our group can only spawn the trio in herd mode when we have six people with all the achievements. When we have five players, Estir doesn't give us the option to summon them. The regular shard of hate we can summon the trio with a partial group, as long as we all have the achievements.
In normal u can spawn duo & trio with 3 flagged people in zone i believe (assuming unflagged people leave zone temporarily) In herd you need 6 on appropriate steps for both Duo and Trio.
