If you don’t one-shot him, Skarrik already has cool attacks and patterns, albeit quite repetitive : he’ll spam his spin attack in the same way Bödvarr Ribspreader will spam his slam ; but he also switches weapons and has completely different patterns depending on whether he has halberd or dual-wielding.
How interesting would it be if he had a stamina mechanic, i.e. he parries attacks until we break his stamina, and back attacks deal more stamina damage. His special attacks (like the knockback spin attack) would cost him some stamina (like a player push attack) but give him time to recover some, and ranged damage would still damage him but with some good DR.
Without changing him too much, by giving him some immunities that can be overcome (as he’s vulnerable once his stamina is depleted), without it being too spammy (I don’t like boss mechanics that revolve entirely around minions, it removes personality from the boss himself ; but minions are needed otherwise the boss doesn’t feel like a faction leader).
Maybe once his stamina depletes, he can take 1/3 of his health in damage before recovering instantly and switching weapons.
Why not start off phase 1 with his halberd and stamina mechanic ; phase 2 enraging, dual-wielding and behaving more like a plague monk and where he’s immune to stagger and ignores the stamina bit - or rather he doesn’t parry at all ; and finally phase 3 where he senses he’s in trouble and takes out a shield (where he has more stamina) and perhaps calls out more minions to his help.
His minions would all be stormvermin (with some trash rats in between as fodder) ; halberd ones in phase 1 and shield ones in phase 3. Phase 2 could be his ‘solo’ phase, where he’s harder to handle for the team and way more erratic in his aggro, dealing high damage and high stamina damage.
He could be supported by ratlings and globadiers throughout the fight ; I’m picturing 2 ratlings on the heights around where he spawns from and why not scripted globadiers that don’t target a player specifically but quarters of the arena ?
In higher difficulties it would be challenging to add plague monks during phase 2 or 3.