Spoilers: Clan Rictus, the war-declaration tools, and the qualifying packs. No campaign ending.

A warlord who survives the warrens
Tretch Craventail is Skaven Free-LC. The qualifying ownership is Warhammer II, The Prophet and the Warlock, The Shadow and the Blade, The Twisted and the Twilight, or Thanquol — Lords of the End Times, on the same storefront as the campaign. He leads Clan Rictus. The new-player FAQ is the studio's note that a race pack and its free lord are not the same purchase as every other paid lord of that race.
He rose through Clan Rictus by guile and treachery. Escaping a disaster is as much of the reputation as winning the fight. He is a melee lord. Skrolk is the plaguelord, Ikit is the engineer, and Thanquol is the Grey Seer. Tretch is the survivor of Clan Rictus.
What declaring war turns on
Declaring war activates Clan Rictus's temporary attack bonuses. The lord page names them: improved ambush prospects, Vanguard Deployment, and an extra use of The Menace Below. The armies have to be ready before the declaration, or the opening expires on a force that cannot use it. A favourable battle is the point. A declaration that uncovers several settlements is the mistake the same page warns against.
Clanrats hold space for a flank march. Stormvermin support the attack or the approach that is about to fold. Tretch stays near friendly troops so he can leave. Queek's Menace Below is a food purchase before battle. Tretch's extra use is tied to the act of declaring war. Same summon, different switch.
The clans he is not
Ikit's workshop, Snikch's contracts, Throt's laboratory, Skrolk's plagues, and Thanquol's Masterplans are the paid or later Skaven campaigns. Owning one of them can be the qualifying route that makes Tretch free. It does not give Tretch that clan's system. Clan Rictus keeps the Under-Empire tools the race shares, plus the declaration bonus.
Queek's Eight Peaks war is Headtaker and The Rise of the Horned Rat. Thanquol's books run from Skavenslayer through Grey Seer. Tretch's campaign is Clan Rictus: the qualifying packs, the declaration, and the habit of leaving. A war you declare for the ambush bonus is that opening. It is not a chapter of Queek's or Thanquol's novels.
Tretch Craventail: gameplay and availability · More character stories
Sources
- A new player survival guide and FAQ — community.creative-assembly.com
- SEGA: Immortal Empires DLC Ownership Guide — support.sega.com
- Immortal Empires DLC Ownership Guide — SEGA — support.sega.com