Lads I need help, I've been trying to attempt a solo 1 character only run on vanilla honour+tactician (without single save slot) as Dark Urge Gloomstalker 5 Assassin 3. It has been a breeze so far but I have been totally stonewalled at Apostle of Myrkul. I've tried everything I could come up with.

>deal enough damage over time to his 390hp pool
>he heals for 30 per infinite minion
>the less minions there are the more he can spawn
>if minions get stuck he does AoE pull to get them out or kill them
>blocking ladders doesn't matter for same reason
>one-two shots any summon I have
>if I hit him myself I become permanently rooted

Any advice welcome except getting more characters which is haram for this run. I can load before entering the colony and respec.