Monster sizes (サイズ, size) are an aspect of the Monsters series that dictate how many party-slots a particular beast will occupy, with one exception.
Each breed of monster has a fixed size that is displayed on the corresponding encyclopedia page, ranging from S, M, L, LL, & G. Instead of party slots, these sizes determine a monster's evasion rate in battle.
The size concept was given a complete overhaul for the second Joker game, setting the standard for all subsequent titles. Being a major selling point for the title, several new monsters were designed to illustrate the concept and feature as boss battles, such as the wormonger. The size ranges are small, medium, and large: the former is the average size for monsters and takes up just one party slot, with the latter sizes taking two and three slots respectively. Medium-sized monsters enjoy a 120% increase to the damage dealt by abilities that are not classified as slash-types (Assassin's Stab, Gigaslash, Kacrackle Slash, etc), while large-sized monsters see a 150% increase to the power of non-slash techniques and slash-type skills now target all enemies.
As a general rule of thumb, medium-sized monsters will have higher maximum stats on average while large-sized monsters will have considerably more HP than their smaller peers. Due to taking up multiple party slots, medium and large monsters will typically have the Tactical Genius and Tactical Trooper traits to act multiple times per turn. An important note is that monsters sizes are treated as a "family" of their own, meaning that a monster with the Giant Killer trait hits a Bjorn with the Beast Bopper skill, the behemoose will suffer cataclysmic damage.
The number of monsters that may be in the party has been increased to 4, allowing players more freedom in developing their teams. Large-sized monsters now see only a 130% damage increase in non-slash abilities.
A system has been introduced that allows players to change the size of their monsters, allowing for greater party customization. Additionally, an extra large category of monsters was introduced which occupies all four party slots, which see a normal attacks and slash-type skills deal 110% damage on top of targeting all enemies, the power of spells and non-slash skills increases by 130%, and maximum HP/ MP is 250% that of a small-size counterpart.
Large-sized monsters' damage increase to non-slash skills has been reduced to 125%.
Monster sizes have been greatly simplified for player convenience, being only 1-slot small monsters and 2-slot large monsters. Among the gameplay differences is that larger monsters will gain three extra traits: two are automatically granted at level 1 while the third is unlocked at level 60, and one of these is always part of the "Tactical" set so that the beast can act multiple times per turn. Large monsters also enjoy 50% more resistance to confusion, instant death, poison, paralysis, sleep, and being stunned.
One crucial point for considering using large monsters in one's party is how their stats compared to a smaller counterpart. Large monsters will have 25% more maximum HP & MP than a miniature counterpart of the same level, while their other stats will be multiplied by a variable determined by which Tactical-class trait they possess:
This means that certain monsters be considerably weaker overall than their smaller brethren, and careful consideration to their talents and accessories will need to be taken into account before being added to a team.
Any monster breed can be adjusted to large or small size via monster synthesis, with the rule of thumb being that sizes will scale downward unless one of the two component monsters is already large, and had two large-sized monsters as it's own components.