With mechanical drop sets, instead of dropping down to lighter weights when you reach failure, you keep the same weights but switch to a related exercise where you have a mechanical advantage. This allows you extend the set, triggering metabolic stress and increasing time under tension, both crucial for hypertrophy.
Here's an example for arms:
Start with 8-10 Zottman curls. Curl the weight up normally and then rotate your wrist into a palms-down position to lower the weight.
Now do 8-10 hammer curls without resting.
Finally, rep out with 8-10 alternating dumbbell curls.
It was a dire situation, a nightmare of indescribable proportions that only Dante could relate to. Every salacious thought I've ever had and every misdeed I ever committed was paid back to me in spades.