One time I won an ebay lot with a bunch of old D&D stuff and it had a deck of Monster Cards. I never saw these back in the 80's and didn't even know they existed until the lot arrived in the mail. A pleasant surprise to be sure.
Reading through the cards I can appreciate how well done they were for the time. Excellent full color art and full descriptions and stats on the back. Upon closer inspection they also have minor improvements over their original entries in the Monster Manual. Perhaps the best addition being they provide statistics for the XP value of defeating the creature. Changing the numbers from ranges (ie. 2-12) to dice rolls (2d6) was probably just a bit easier for quick reference during play, it is a minor thing to convert 2-12 in your head to 2d6, but at a glance it makes for a quicker read.
Changing terms like "offal" and "carrion" to "garbage" and "carcass" is another minor improvement and these subtle changes to the language that is used reduced the reading level of the vocabulary just a bit, making them more universal. At this point elementary school age kids were playing the game.
These cards were published in 1982, a year after I started playing. I sure could have used them back then as a great playing aid!
Here is one of my favorite creatures to use at lower levels, the humble bombardier beetle. It's always fun to add sound effects when they fire their deadly vapor cloud.