In my free time I play against myself (my Eldar) using Vassal (a
40k simulator).
I do this both for fun and to learn something new at home and not at a tournament. Usually this ends in a lost game.
After fighting nids (4 Flyrants, 3 Tervigons, Doom) I realised that I have some serious problems against armies that tend to get in your face.
That probably also includes deamons but due to my lack of skills playing them I usually just obliterate them and that doesn't teach my anything.
My next list to beat (or be beaten by) ended up being so funny/strange/out of the box/put there some other adjectives/spammy/competetive? that I just had to post it.
You can possibly swap Plague Marines with more Cultists.