Killing legislators or physically threatening them into overturning the results. But siccing the mob was just a last-ditch move.

The main plan was sending fake electors with fraudulent certifications and counting on Pence to derail the formal vote count and accept the false slate through a fog of procedural confusion. The fact that Pence refused to go along with the plan and Trump resorted to physically threatening him and Congress doesn't change the fact that their plan was an illegal and fraudulent interference with the verification of the election based on knowingly false claims.