Monster modifier

Monster modifiers are additional traits that monsters can have, usually making them more powerful. They come in two known varieties: some, usually called prefixes, appearing before a monsters name (like Champion) and some appearing below a monsters name, called titles, like Doppelganger. Uniques almost always have a modifier- in fact, it's so far been quite rare for a non-unique to have a modifier.

Most known information about Monster Modifiers comes from Zagreus's forum post, seen here. An official post about Monster Modifers is supposedly coming in the next few days.

Known Prefixes

Champion:

Fanatic:

Possessed:

Known Titles

Electrified:

Plagued:

Fast:

Magical:

Frozen:

Stoneskin:

Cold Aura:

Doppelganger: The Doppelganger title causes an enemy to create duplicates of itself, similar to the Wizard's Mirror Image skill, that do damage, until the enemy is killed. The duplicates are assumed to not spawn duplicates as well.

Molten:

Powerful:

Thousand Pounder 'Title'

The title 'Gluttony Incarnate' is a mystery. Comparing this big fella with the Siegebreaker Assault Beast, he seems to have a 'title' that would work very much like Diablo 2 Monster Modifiers. Still, 'Gluttony Incarnate' could be his title just like the Siegebreaker's 'Living siege Engine of Hell' obviously must be. The Thousand Pounder could also very well be an equivalent of a Diablo II Superunique, with a different name than other units that look the same (as the Thousand Pounder has been depicted to come in packs in concept art). Time (and BlizzCon) will hopefully tell.

Further Reading

You can follow these links for more information on the topic:

• Diablo 3 Basics - All known info in brief.
• Monsters - All known monsters.
• Media Coverage - List of all interviews, previews, images and videos presented by gaming media.