The AD&D 2e Monstrous Compendium came out in 1989 with the publishing of AD&D Second Edition.
It came in a large binder, had loose leaf pages, with enough space to add monsters from the Appendices TSR later put out.
The Monstrous Compendium was meant to be an easy-to-use technology at the tabletop in the days before the widespread use of computers and the Internet. But many people didn't see it that way, they wanted a book.
So did I. I'll be the first to say that I didn't like it. The binder was cumbersome to lug around. Perhaps TSR was being cheap--printing a binder instead of a book and making players buy both Compendiums I & II to have a "complete set" of monsters. And sometimes those sheets were just hard to organize when TSR would put say, a "B" monster on the same sheet as a "C" monster. Yeah.
But I'm not going to focus on that. In fact, from here on out, whenever I do a review or retrospective on 2e product, I'll focus on the good stuff. Because there some gems to be found... if you just dig a little.
Well... I'm digging.
Because I'm sick of AD&D 2e not at least sharing some of the spotlight in the OSR, being condemned for not having Gygax at the helm, criticised for railroad adventures, Thac0, splatbooks, and blah blah blah. If you're dismissing AD&D 2e for any of these reasons, then you're missing out of some cool stuff, because somehow it worked.
Anyway, back to the Monstrous Compendiums...
Here are the gems:
DMs can customize the monsters they use. If, for whatever reason, you don't use ogres at all, you can put them in the back of the compendium or take them out all together. You can build your own selection of monsters for your homebrew campaign setting, and separate the others.
DMs can take a monster entry out of the compendium for quick reference at the tabletop. A dragon, for example, uses lots of rules. Instead of having a manual at the table taking up space, you just have a sheet or two of paper to reference. You can also highlight abilities and tactics without fear of ruining an expensive book.
You can also hide these entries better from your players behind your DM screen. Players can anticipate an encounter when you reach for a monster manual.
The dividers feature full color artwork. Yes, this artwork has been recycled from other products. But it can be easily used for your games to describe a monster, NPC, or cool scene.
This binder system can be used with other products. If you still have those old BECMI books then can put alongside these monsters. TSR also released Treasure Maps to be used in a 3-Ring binder. If I recall, some of the Role Aids line by Mayfair Games (Denizens of Verekna?) also used the same format for their monsters.
The monsters have been updated from AD&D 1e. This is the most obvious gem. But wasn't calculated XP based on hit points getting old--especially since the old Monster Manual didn't have XP for each monster listed? (Their XP totals were in the back of the 1e DMG).
I'll let you decide if the full page writeups with ecology sections are gems or not. The ecology sections sometimes contain adventure seeds.
One final note: Some of these monsters, even the Piercer, didn't make it into later editions--especially ones from the later appendices. So you might want to hang on to your Monstrous Compendiums for in case you had a odd monster not supported by the latest edition of D&D.
So those are the gems of the Monstrous Compendium I & II.
I don't have my copies anymore, so my apologies if this wasn't a thorough enough review. You'll find out what happened to them on Day 17 of the D&D 40th Anniversary Challenge.
I still own, however, the appendices for Dark Sun, Ravenloft, the Fiend Folio, and Greyhawk. So you might see reviews of those soon--especially the Greyhawk appendix.