Monsters have various characteristics such as HP, MP, actions per turn, cards per turn, etc. These are fairly standard across all monsters although certain ones are flagged as "extra HP" or "extra fast" or "extra gold" etc...
Here's a rough guide:
GRIZZLY BEAR Edit
Gold gained is normally 1-4x the XP gained, (between 2-3x most of the time).
Bosses get a 4x XP multiplier, an extra card every other turn, and often a large HP multiplier (see each boss page for details).
Same as above but all monsters have 90% starting health.
Your character gains 1 fewer HP each level.