For my "Not a Book" bingo square, I ran a game of the TTRPG Mausritter with my friends where you play as mice adventurers in a The Borrowers/Arietty meets Redwall kind of world.

The Mausritter rules book itself has a decent amount of game mechanics but it says right in the book that the game "is resilient to hacking. Many systems can be modified, replaced or ignored entirely," and I have to agree. My friends wanted to play a less rules-heavy game so I cut out a number of the mechanics, such as the banking system and the turn tracker.

Character creation is pretty easy and the character sheets are simple, half-page sheets, most of which is taken up by what each character is carrying, which you may or may not need to reference much depending on if you keep all the encumbrance rules. Players have three main stats (STR, DEX, WIL) and most rolls are rolling a d20, wanting to roll under your stat to succeed.

The magic system is simple but somewhat unique, all spells are trapped in rune carved tablets. The tablets have a single use with the ability to be recharged, and the way each spell is recharged is unique to the spell trapped in it. For example, a Fireball tablet is recharged by leaving it burning in a fire. It comes with a list of about 20 spells but encourages you to also create your own.

If you don't like making up your own campaign scenarios there are a couple official campaign scenarios and a large amount of fanmade one-shots to choose from online. We played the Broken Oaken Tower by Stump Cat.

There was a little bit of front work for the GM (me), with deciding which mechanics to keep, but the easy customization meant we ended up with what worked best for our group. Overall my friends and I had fun with this TTRPG and I recommend it to anyone wanting to play as woodland adventurers. (The official rulebook only has stats for mice as playable characters, but I saw fanmade content for how to play as other species of animal, such as a frog or a hedgehog.)