After experiencing a combination of different pokemon, I finally found the team I love the most that helped me get through the ranks of Battle Royal and even won some Online Royals. Now I use the team for almost everything. I do get Nebby out from time to time as well, but I don't use it anymore. I did use Battle Bond Greninja and Nebby for the Elite 4, mainly because Nebby is part of the storyline, so I didn't want to break the storyline.
Male Crabominable (Lv. 74)
Ability: Hyper Cutter
Nature: Impish
Item: Icium Z
Ice Punch, Ice Hammer, Crabhammer, and Brick Break.
Male Mudsdale (Lv. 58)
Ability: Own Tempo
Nature: Docile
Item: Soft Sand
High Horsepower, Earthquake, Heavy Slam, and Focus Blast.
Female Salazzle (Lv. 70)
Ability: Corrosion
Nature: Modest
Item: Poison Barb
Sludge Bomb, Sludge Wave, Dragon Pulse, and Flamethrower
Male Decidueye (Lv. 82)
Ability: Overgrow
Nature: Jolly
Item: Decidium Z
Low Sweep, Spirit Shackle, Leaf Blade, and Shadow Claw
Female Lycanroc (Sun) (Lv. 77)
Ability: Sand Rush
Nature: Impish
Item: Black Glasses
Crunch, Brick Break, Rock Slide, and Stone Edge.
Female Goodra (Favorite of the whole team) (Lv. 55)
Ability: Hydration
Nature: Hardy
Item: Dragonium Z
Thuderbolt, Ice Beam, Flamethrower, and Dragon Pulse (Soon to be Draco Meteor)
I found that it was better to have tanky and hard hitting pokemon for Royal. As if you are fast and hard hitting, you don't usually get to take out the opponent and you tend to be knocked out quickly.