The Frost Gate (Hard Mode)

Builds

The mission has space for six people. My party included:

1. Myself
2. An offensive mesmer
3. A protection/healer monk
4. A support N/Mo
5. An SoS Meta ritualist
6. An ST Meta ritualist

Small side note: the URLs above do not display the builds perfectly. I don't use toxicity for example, but Rending Touch instead.

First note: whenever there are Dolyak Healers, use skills to remove their enchantment. For my party the Stone Summit Sages are a pain in the butt. So kill those first.
Everything will be easy until you're near the bonus part. First I cleared all enemies that are waiting between yellow point 2 and 3 as depicted on the Wiki page. Make sure to aggro enemies so they don't come all at you. Another strat would be to summon ritualists' spirits before engaging. Once you cleared all the enemies, then start with the bonus objective.
Lastly, I finished the mission with the alternative strategy described on the Wiki page. That's all!