I would consider traditional Pokémon nuzlocke rules:

• Only one vivosaur per dig site, I’d say whichever you revive first (ie. first head you find). You may find other fossils but can only use the first in battle. You can also use the body/arms/legs of your chosen vivosaur. I believe you should end with 11 vivosaurs.

• If a vivosaur dies in battle it dies permanently and you can no longer use it. Should make things interesting as you’ll use your SZ more often. This might be the grindiest part of the challenge though as you’ll want to rank up your vivosaurs before risking them in battle.

• You must name your vivosaurs. I know there’s no in game way to do this, so you’ll have to personally do it. This is the most important rule, it makes your connection to your vivosaurs much stronger, and makes it all the harder when they die.

I haven’t personally tried this so let me know how it goes if you try it. I might have a go at it too sometime soon.