Early game · first 8 minutes
Throw Powder Keg beside Rat King and shoot it to detonate it before he can move away. Keep a dash for any rats that attach while you are aiming.
Holliday vs Rat King
What's giving you trouble?
Full matchup plan
Mid game · Walkers
Damage Royal Pestments with Powder Keg while staying near cover. Keep Bounce Pad ready to get away if Rat King runs toward you with the banner.
Late game · Patron
Place Bounce Pad between you and your teammates. After Royal Pestments ends, drag Rat King toward them with Spirit Lasso and use the pad to extend its duration.