Nice! I like the skills, the simple mechanics, and the lethality. d4s always have a fun resonance for playing little critters, as well. I initially thought that the list of skills was a table to roll on, as in to select the qualities, rather than what you meant which was an array of stats… maybe ‘for each stat’ would work better than ‘to determine stats’? (Same word count)
I feel like the multi-game progression lends itself well to playing this for like fifteen minutes as a warmup game with whosoever arrived early/on time before the main game of the evening; over the series of evenings I can imagine some rats getting large enough to start getting noticed by the characters in the main game!
Clever name too! Simple but very memorable.