Mobs are listed and classified by their nature in regard to the player as below. For more details on a particular mob, click and view their individual page.
Pets that can be summoned by the player, but are non-attackable and passive mobs in-game. These pets cannot attack mobs, but they still take damage and are affected by player auras but they won't die. Player can upgrade to Hero Pass to collect them.
The special mobs are unclassified. They have special spawn generations, or have the same behavior and appearance with other mobs to make players confused.
The mobs only have their name in the game data file. Unlike unused mobs that have in-game textures, sounds, or appear in the official trailer. Most of these mobs are based on mobs from various editions of Minecraft.
Some mobs from original games have new features in Minecraft Dungeons. For example, many mobs have sound files for behavior animations named "Novelty". All mobs except the Heart of Ender have animation when idle, though many don't tend to see them or document them. [1]
When mobs die, their body turns gray then fades into dust.
If the player's enchantment is used by mobs, some of the enchantment's effects would turn them purple in color. [2].
Ranged mobs tend to have more health then Melee mobs, this might be because their attack speed is very slow or their attacks deal little damage. They also tend to flee from the player when not attacking.
The mob's HP increases on higher difficulties for recommended power levels with 1 (power level on each difficulty) = 1x (x = times the multiplication), so 4=1.7x, 10=2.7x, 16=4.1x, 22=5.5x, 27=7.4x, 33=9.9x and so on.
If any mobs were 32 blocks away from the player, their animation will stop to prevent the game from crashing.
Bigger mobs doesn't ALWAYS mean they have more health then others, for example, the Jungle Abomination is the current largest mob in the game but doesn't have the most hp because the Mooshroom Monstrosity has 20% more hp then the Jungle Abomination even though it is slightly smaller in size.
References
↑Example, Necromancers and Enchanters throw their staffs and books in the air then catch them and celebrate.
Skeletons will spin their heads around when idle. Zombies will slouch over, Baby Zombies will dance in position, and Cave spiders will do a backflip.