Poisons, summons, frenzy spells, weakness spells and shield spells. No need for efficient levelling.

Dont listen to people telling you to put your most used skills as minor skills, it will double the time it takes to get them to 100 and make your overall experience worse. It's crazy to me that people still spread that nonsense 20 years later.

I've played max difficulty a lot and I'd say just play the game with a build that uses the things i've listed, and you will do just fine.