Also called a "monster encyclopedia" or "bestiary", this is a feature of various RPGs that allows you to review the types of enemies, monsters, and beasts (if not more) that you've encountered, battled, and slain throughout your quest to Save the World. This is related to the Enemy Scan, except that while the Scan is a tool you use during actual combat, the Monster Compendium is a reference guide for you to peruse later at your discretion.
The amount of actual information shown on a given Monster Compendium page varies from game to game; it can range from mere Flavor Text to a full blueprint of the enemy's statistics (including elemental affinities, money and item drops), possibly even tips for battling them more easily.
As a rule of thumb, Monster Compendiums always start as an empty book, with information on each monster appearing only after you've actually encountered a monster "in the wild" (this avoids spoiling the player about future monsters or, especially, Boss Battles to come). Sometimes you must actually slay the beast before it will appear on the Compendium's pages, or you need to register it by using your actual Enemy Scan; on the other hand, sometimes merely spotting the beast on the field is enough to unlock its corresponding Compendium entry.
Achieving One Hundred Percent Completion on a Monster Compendium (i.e. registering every enemy type in the entire game) is tough work—some monsters, like the Metal Slime, are naturally elusive and thus difficult to register an entry for (especially when you have to slay them); different variations of the same monster archetype might have different Compendium entries; and most annoyingly, some monsters only appear in specific places (or times) and their Compendium entries can become Lost Forever if they aren't scanned or slain (or otherwise registered) at the first opportunity you get to do so. Fortunately, completing the Compendium is always optional, although some games may actually reward the player (in some manner) for full completion.
- The Digimon Analyzer is basically this.
- As mentioned below, the Pokédex appears in the Pokémon anime, and, at times, was of use to the protagonists beyond merely identifying species of Pokémon. In one instance, it served to ruin Meowth's disguise, as it identified him as a Meowth (rather than the Sunflora he was dressed up as).
Live Action TV
- Airwolf has a database on board that does this thing.
- Pretty much every Pen and Paper RPG ever conceived has additional material in the form of "Monster Manuals". However, they aren't available in-character; they are reference material primarily for the Game Master's world-building.
- Much more common in fantasy, space fantasy, or sci-fi RPGs than in modern horror or historical, where the antagonists are usually the same things as the NPCs. The Trope Namer is the old Dungeons & Dragons Monstrous Compendiums, which in the game's earlier editions were batches of monsters specific to different themed settings that were sold in a packet.
- Making lore checks allows players to make an Enemy Scan of sorts in Dungeons & Dragons.
- The Suffering has detailed entries of all freakish enemies in both games.
- Final Fantasy didn't always have these, but the remakes of I through VI have them, as do some of the newer games.
- Chrono Trigger also got one for the remake.
- And many more... let's just say Square-Enix is fond of this feature.
- Final Fantasy XII in particular, is known for its heavy use of Purple Prose and Antiquated Linguistics in its monster descriptions. Killing a certain number of a given monster unlocks further monster lore, usually about whatever Loot item the creature drops. The lore gives implications that several monster species (like the early-game werewolves, and Malboro Kings) used to be humans, and there are many ways that a slain person will later rise up as a zombie of some variety.
- Paper Mario: The Thousand-Year Door has one, though scanning in the first game (as well as the second) also provided a permanent benefit in that you could see the health bars of all further enemies of that type you'd encounter. Thousand-Year Door also avoided one or two time entries being Lost Forever if you checked Professor Frankly's trash can.
- Super Paper Mario turned this feature into a card collection sidequest. Monster cards didn't only detail its stats but also gave you an attack boost against it. Cards drop from enemies but can also be bought at stores... in true TCG-style booster packs.
- The Pokémon games, like the anime, have the Pokédex. It lists every Pokémon you've seen, and gives more details on the ones you've actually owned at some point (even if you've evolved, released, or traded them since). Since the series's third generation, all games begin with a regional Pokedex listing only the Mons native to an individual region, and upgrade it to the National Dex later (usually after beating the game), which lists every Mon in the series up to that point.
- The Pokémon Colosseum games do not give the player a Pokedex, but a "P*DA" instead which performs similar functions: The "Snag List" / "Shadow Monitor" options display information relating to Shadow Pokemon only, while the "Strategy Memo" displays information about any Mon the player has seen in battle. Like the Pokémon Stadium games before them, the player can also view and rotate the Mons' 3D models from any angle.
- The Pokémon Ranger series do not use a Pokedex either, but give the player a "Ranger Browser" which logs every Mon the player has defeated ("captured") in battle, and can search through them according to a Mon's field move or elemental Assist type.
- The log function in the Metroid Prime series records not just enemy information, but almost anything you can scan, including item pickups, puzzle mechanisms, local/ancient lore, and so on.
- Dragon Age and Mass Effect both have a giant encyclopedia called a Codex that tells you everything you need to know about the setting.
- The free MMO Atlantica Online has an interesting variation in that each enemy of a type you kill has a chance to give you its Monster Info, split into three parts: General, Location and Items. Getting the complete Info also increases the amount of items dropped. The Info can be shared between players and is sometimes required for a certain quest, probably the most concrete use of this trope in gaming history. The game additonal also offers tons of information about NPCs, items and other points of interest without the need to unlock it (though information about which monster drops items is obviously tied to the Monster Info).
- Mother 3 has the Battle Memory, which not only gives you info on all the enemies, but lets you practice fighting them in safety. Collecting all of them (including the front and back sprites) unlocks some extra features.
- The X-COM games have the UFOpedia, which contained information on the enemies you had researched after capturing or killing them, as well as their ships, their weapons, their useless but interesting technology, and their society. It also contains all the relevant information on your ships, weapons, items, and base facilities, making it the one-stop-shop for any info you're looking for.
- The Tome of Knowledge in Warhammer Online keeps track of the types and numbers of monsters you've killed. Killing certain numbers of them will sometimes reward the player with things like titles.
- Shin Megami Tensei II had the demons you ally stored in the Compendium. This trend continued throughout the entire franchise, and has gameplay purposes beyond being a mere bestiary: as you fuse together your demon allies, the original ones are lost. However, if you recorded your customized demons in the Compendium, you can summon them again and again as long as you have the funds, and use them once more as allies or fusion fodder. Additionally, more recent versions of the Compendium explain the mythology behind each demon.
- The original Devil May Cry contained elaborate monster descriptions which grew more detailed as you fought them, recording every attack they used against you. The sequels also have monster compendiums, but they only have short descriptions.
- Tales of Symphonia gave Raine a title if you filled in 100% of all enemies. Fortunately, an enemy is logged in the book without scanning, so you don't need to scan any of them to get the prize. It's still a good idea to scan them, though, as it will give you information that simply seeing them won't (Health, Weaknesses, etc). However, to truly complete the book, you need to use Raine to scan them. Otherwise, you'll lack their location info.
- Repede of Tales of Vesperia had an ability that let him use a single Spectacles to scan every enemy in the enemy party, and another one that displayed the health bars of enemies that had been scanned.
- Planescape: Torment had a detailed and illustrated encyclopedia of just about anything you encountered in the game, enemy or not.
- The Atelier.
- Ratchet and Clank: The second game features one.
- Shadow Hearts has the Library, which adds entries for every monster you encounter. Covenant and From The New World add their stats and other pertinent information if you take the enemy's picture. There's a reward for getting every enemy; since the game is counting the Final Boss you have to get it on a New Game+.
- Eternal Darkness has the highly memorable autopsy reports conducted on anatomically impossible creatures by a man losing his mind from dealing with them.
- The World Ends With You keeps a database of all the Noise you've defeated. It also lists the pins that they drop, combined with the difficulty required, and drop rate. Of course, you actually have to have defeated them at whatever level for it to list. Cue a lot of players getting frustrated at Sho Minamimoto, and the various Elephant Noise.
- All modern Castlevania games have this, except Circle of the Moon, which doesn't count anyway.
- Several games in the Wild ARMs series have this.
- R-Type Final has a compendium that slowly fills as you rack up kills against those enemies.
- Dragon Quest:
- The DS remakes of IV, V and VI have the Big Book of Beasts, which shows you every type of enemy you've fought, as well as how many you've beaten, how easy they are to recruit in V (though you shouldn't trust those chances too much), what items you've gotten from them, and their in-battle sprite. You can even press A to see their attack animations.
- VIII has a similar monster list, which also shows their character models and allows you to see their attack animations. Completing the monster list by defeating one of every monster (including bosses) netted you a secret item that would eliminate random encounters.
- IX had the defeated monster list, which showed the models, animations, and obtained drops of all the defeated monsters. The Thief ability "Eye For Trouble" added a second page of flavor text and revealed all the items the monster can drop.
- The VGA remake of Quest for Glory 2 adds a monster compendium to the game, which offers a lot of hints that are very useful due to the upgraded combat system. A new side-quest is also added to the game, and the compendium is the reward for completing that quest.
- Okami has an encyclopedia of monsters you encounter, all gorgeously illustrated. It also provides hints on any weaknesses the monster might have.
- Sabrewulf provides two compendiums, one for "good creatures" and one for "bad creatures." Since the game emphasizes avoidance over combat, you get information on the latter as soon as they appear rather than having to defeat them first.
- The Legend of Zelda: The Wind Waker features a sort of beastarium composed of statues of all the enemies (and the NPCs, too) with short descriptions of each. So how do you fill this out? Three statues at a time, one a day/night cycle. Figures.
- Operation Salvage, the video game based on the Walking With Beasts series, includes a database which the player helps to fill by scanning animals and enemy equipment. It also includes information on your equipment, the plantlife in particular time periods, and a lot of other related information.
- Built up over multiple plays in Angband. Your characters are assumed to pass down a log of their experiences. The first time one of your characters runs into a monster, you get minimal information. As you encounter more of them, do damage, and take damage, the log automatically fills with lower and upper bounds of damage, AC, and hit points.
- Endless Ocean has a non-violent version of this, as the player's whole role (before you start receiving threatening e-mails that Vagueness Is Coming) is to catalog the various creatures found around a fictional south Pacific coral reef. You do this by interacting with them.
- MARDEK has an included Bestiary from its Encyclopedia section, which also includes other information obtained throughout the game.
- The Flash game Bubble Tanks 2 has this. One of the enemies (Sapper Fighter) was unobtainable, however, as a bug in the game made it such that it never appeared at all.
- The Gundam PlayStation 2 RPG MS Saga: A New Dawn had one for all of the bad guys and it was possible to get all but one due to being out of the way and only available during one part early in the game.
- The console-based Super Robot Wars has one for all characters and mecha, both good and evil. Even more, the pilots tend to have soundbites you can play where they say popular phrases. The same goes for its Gundam-only counterpart G-Generation.
- Kirby 64 The Crystal Shards had a series of cards which could be collected at the end of a level. They depicted the monsters of the game, including the bosses.
- Opoona has the Rogue Book. Completing it is actually a sidequest you can get rewards for, and it's more difficult than it appears—some enemies are vanishingly rare.
- Pikmin 2 allows you to not only view and read information about the creatures you encounter, but also throw bait at them to see how they would react to your Pikmin.
- And then Louie keeps an alternate log relating to how best to prepare the creature in questions as a delicacy (if it's possible to do so).
- In the Bionicle video game; Maze of Shadows, there is one of these in the game that fills up with entries after you defeat the monsters.
- The Witcher has an extensive bestiary. Note that you have to acquire that information first through various means. The entries give tips to the monsters' weaknesses and many body parts/alchemy ingredients you can only collect if you have the appropriate entry.
- The Touhou Universe Compendium Perfect Memento in Strict Sense is also one of these, the only official source for information on the various Youkai that inhabit Gensoukyou.
- Yoshi's Island DS has a museum of enemies (obtained by defeating them with an egg).
- Serious Sam's NETRICSA provides this for each new enemy Sam kills, except the bosses, whose description pops out as soon as they do.
- Wario Master of Disguise has a subsection on the treasure guide that lists every enemy Wario has defeated, along with a description of them.
- The Starfy series has these. In the first 4 games, you get entries by talking to friendly characters and defeating enemies (And getting damaged by the invincible ones). In The Legendary Starfy, they are unlocked via a random-chance toy machine, which makes getting the last few entries a pain.
- See the Index of Fictional Creatures.