I believe there is a problem with the premise of your question. If you have done 80+ cases and you still feel shaky, this is a surefire indicator that you have not learnt how to solve cases in the right way. Practicing is something that is needed and helpful during the phase when you build your case solving muscle, i.e., when you learn how to think through complex problems, how to set up the logic to answer the core question asked, and how to navigate through this logic. Once you have understood and internalized this, then you don't need excessive practice anymore. Just two or three warm up cases before the actual interview, and you're good.
But for this, the precondition is that you learn how to properly solve cases:
- This does NOT mean learning frameworks.
- It also does NOT mean learning industry facts.
- And is also does NOT mean practicing speed of complex mental calculations.
It just means you have to internalize the skill of applying rigorous top-down thinking to complex problems. Once you master this, all the rest (communication, calculations, synthesis etc.) is pretty easy to train and anchor. But the principles of top-down thinking are the fundamental base for building the ability to address ANY question in a robust way.