"These enraged, oversized fallen creatures are bloated seemingly to the point of bursting, an impression buttressed by the fact that these insane demons rush their intended victims and then stab themselves until they explode. A more fitting name could not be found for these maniacal beings."
Fallen Lunatics are a type of Fallen.
"The fallen lunatics are the most unstable of their kind, causing them to overproduce highly combustible fluids in their abdomens. I believe this imbalance must be inevitably fatal, leading the lunatics to puncture their stomachs and release their explosive bile in a terrible display when enemies come too near."
The Lunatics are large, bloated Fallen creatures. The most unstable of their kind, this leads them to produce highly combustible fluids in their abdomens, one that Abd al-Hazir believed was inherently fatal to the Lunatics. These insane demons rush their intended victims and stab themselves until they explode in a shower of bile.
Fallen Lunatics debut in Diablo III.
Fallen Lunatics return in Diablo IV.