How? (a) bought Mausritter and the campaign box The Estate in a charity bundle; (b) recently got done playing a few episode game of Mausritter.
What? You are mice and the world is deadly. Very much a product of the OSR and post-OSR scene, which means:
* no combat rolls, you automatically hit (maybe from Into the Odd)
* spells can be recharged (from... Goblin Punch)
* when you get hurt, you take damage to your ability to carry inventory (from Knave).
That's mechanical; the philosophical angle is: you may very well fail and die -- and that's fine, because you can roll up another mouse. Also: rolling up a mouse is sort of fun.
In my play group, the proximity of death and the randomness of encounters was kind of a problem, but I dug it because vulnerability seems reasonable for mice.
And then, to show you how to play a campaign, here is The Estate.
Yeah, so? First, I find mice heroes against a world of cats and rats and beetles to be pretty charming and nicely done. How do you model cats? Oh, they're like dragons or like buildings: they are warband scale, immune to the attack of any single mouse.
The Estate is just that: a house on some grounds with several factions: the clock-spider, the magician cat, the gang leader, the thieving magpies. And several different trifold pamphlets detailing some dungeon or adventure: the wizard in the suit of armor tower; the boat race to get the blessing of the frog-oracle; the giant snake in the sewer that was the hideout of the rat gang. Add in some random tables, like running across the dung beetles, and you've got this weird, living environment.
Like, there's this epic quest to stop any of the factions from taking over the Estate, including the dictatorial cat who wants to use the Spell of Undeath to eat mice and then raise them as her army; but then you have "the queen's crown fell into the muck, go get it back from the dung beetle home, which is now under attack from spiders." There's also "rescue a mouse from a cage in the house and escape through the chimney" (which starts in medias res, with you trying to get out of the house), "interact with the religious movement in their chapel", "stop the moth queen who has been turned power-hungry by a moldy spore", etc.
There's just so much in here, and all of it seems fun. Like: the slightly unpleasant wizard has an enforcer -- sure, that could be a brute of a mouse, but why not make it a bat who has been cursed with muteness and who the wizard has promised to cure?