A fan asked for details about the bonus item that can drop when you’re playing with a Monster Power setting of 1 or higher. Lylirra provides a useful answer:
Most monsters — like say your everyday shambling zombies — have a roughly 30% chance to drop loot. The exact percentage, however, varies from monster to monster (for example, the Tormented Stingers in Act III have a much lower chance because they spawn in large packs and are easy to kill).
When you kill a monster in Inferno on MP1 or higher, if you pass the initial roll to obtain loot, you will also get a second roll to get an additional piece of loot. The “bonus item” chance for each MP level is detailed here. A few monsters are exempt from the bonus loot, but we tried to put it on the vast majority of normal monsters, and will probably add it to more if we like how the system plays out.
Also, just to be clear, the bonus drop applies to Normal monsters only. We wanted Monster Power to provide players with extra loot rolls, and (since Champions and Rares are already guaranteed to drop multiple items) Normal monsters seemed like the best place for us to add that mechanic in.
Referring to the chart, if you’re rolling on MP4 and bagging normal monsters, every one of them has a 26% chance to drop a bonus item, and you’re getting a 100% MF & GF bonus (above the normal 375% MF cap) on all their drops. That seems fun, even for monsters with 457% of their normal hit points. (Bear in mind that MP0 is much easier than the base difficulty you currently see in v1.04.)