There are four classes of monster in Dark Summoner that correspond to the three Guilds: Impulse (Sin Guild), Covert (Rancor Guild) and Psycho (Tyranny Guild) and a separate class with no Guild, Cypher. They are arranged into the 10 tiers C, C+, B, B+, A, A+, AA, AA+, AAA and AAA+ with C being the most common and AAA+ the rarest. Each Rank has a base level form and an evolved form indicated by a plus (+) sign. Also see Leveling cost and Evolution.
Currently there are over 1480 monsters to be found. Over 490 monsters in each guild.