This is mostly to force me to remember what the heck I have on my tbr and actually read it. The rules I came up with are simple:

1) The challenge would primarily focus on 100 books on my tbr (+ bonus ig)
2) The tbr mountain is split into portions of 10 books per prompt
3) Whether to count from top or from the bottom is up to you
4) From each tenfold you need to choose one book to read for that prompt (ex: you count the first 10 books in your tbr and from those you choose one to read - this is the book for the prompt)
5) You can read more than 1 book per prompt, but in that case the books should be chosen from the same tenfold, minus the one you already read
6) Unpublished (at the time of you choosing out of the ten for a prompt) books do not count