On a recent whim I decided to head into each of the dungeons and see what multiplier is used for monster attack and toughness in each of them. On the wiki there's some implicit assumption that all or most Hard or Vicious dungeons are the same. As I found, Hard and Vicious are general descriptors of difficulty that are only loosely tied to scaling.
In every case (except for when the VT is involved), I found that health and attack are scaled by the same factor. For bosses that are found in multiple locations, I also found that bosses are scaled by the same factor as the monsters in the dungeons. The slight exception is the weak version of Aequitas found in the Northern Desert. I believe he is actually a different base monster (or somehow a special case otherwise), since he does not reach ordinary VT Aequitas stats when the VT is prepped.
The effect of the Vicious Token is to override the native scaling of the dungeon with 160% attack, 200% health. (Beta veterans may remember that for a short, brutal time, this difficulty scaling was actually 200% for both. As you can imagine this was pretty oppressive and made it hard to get level 1 characters off the ground.) This is why an ordinarily-easy dungeon like Rock Garden (three bosses but lots of popcorn and tame 100% scaling) can suddenly become one of the harder challenges with the VT--your resources are suddenly stretched very thin as the monster toughness spikes.
Although I didn't check them all, Class Challenges and Triple Quests have their own scaling percentages, even if they share a map. For instance, Fighter Bronze is 110%, Silver is 100%, and Gold is 90% (amazing how hard those monsters are with no blackspace). Triple Quest 3-1 uses the Western Forest map, but it's scaled at 130% rather than 100%.
EASY/NORMAL
Hobbler's Hold: 80%
Den of Danger 100%
Venture Cave 100%
Western Jungle 100%
Eastern Tundra 100%
Northern Desert 100%
Southern Swamp 100%
HARD
Doubledoom 110%
Grimm's Grotto 140%
Rock Garden 100%
Cursed Oasis 115%
Shifting Passages 130%
Havendale Bridge 105%
The Labyrinth 130%
Magma Mines 130%
Hexx Ruins 100%
Ick Swamp 120%
Slime Pit 120%
Berserker Camp 100%
Creeplight Ruins 110%
Halls of Steel 120%
VICIOUS
Demonic Library 140%
Dragon Isles 140%
Naga City 150% (top)/120% (bottom)
Vicious Steel 140%
Namtar's Lair 150% (underworld 100%)