Monster Types

All monsters in the Kingdom have a classification equivalent to that of a phylum (a.k.a. category). They are:

Monster types are used for the following things:

A Pair of Stomping Boots can stomp monsters into fine paste based on monster type.
A Happy Medium can Siphon Spirits of monster and make spirits (a.k.a. drinks) based on their monster types. Likewise, the Robortender will drop cocktailcrafting ingredients based on monster type.
The Red-Nosed Snapper can track monsters of a specific monster type, increasing their encounter rate compared to other monster types. It will also drop a unique item after fighting 11 monsters of the specified monster type.
An Artistic Goth Kid generates free combats based on the type of the monster that you last fought.
The Ghost of Crimbo Carols can give you a buff that varies depending on the type of monster fought.
You may extract DNA from a monster and synthesize a Gene Tonic based on their monster type.
Monster Manuel shows the monster type for any monster you've defeated at least once.
A Vampyre can Ensorcel a monster, granting a passive effect that varies depending on its monster type.
Curse of Heredity, an Actually Ed the Undying skill, will cause poison damage to a specific monster type for the rest of your run.
Ka coins only drop from certain monster types.

Certain items and skills affect certain monster types differently than others:

Feeding using the plastic vampire fangs will hypnotize dudes.
Torment Plant does physical damage to plants.
bobcat grenades tear beasts to shreds.
4:20 bombs annihilate hippies.
boxes of hammers destroy constructs.
boozebombs take care of orcs.
holy bombs, batman obliterate the undead, as can the Slay the Dead combat skill.
Certain monster types are immune to Infectious Bite, and these same types also do not drop brains during Zombie Slayer runs.
Great Wolf's lice delevels beasts differently than others, and the same goes for
HOA citation pads and dudes.
Balanced antler rerolls beasts (see page for details).

History

Monster categories were introduced with the Pair of Stomping Boots (August 2011 Item of the Month).
In the April 26, 2013, update to Monster Manuel (which added monster types to the combat display), Jick announced that the official term is "category" (not "phylum", which is what the player base had been calling it since 2011).
In the years between the Stomping Boots and Manuel, the official names of the monster categories were not known to the players. We had to guess, using the stomped pastes (and later, the Happy Medium's spirits) as the only indicators. In many cases, the category names we guessed were the same as the official names; in a few cases, they were not.