First time I tried and it didn't work, I dropped it. But today I decided to see what's wrong with it and why it gives an error (my guess was that the reddit page source code was updated), turns out it was a typo in the formula given in knowledge base:
$tv(reg, wg("https://www.reddit.com/r/EarthPorn/.rss?refresh="+df(D), url, "i.redd.it", 0), "&.*", "")$
needs to be..
$tc(reg, wg("https://www.reddit.com/r/EarthPorn/.rss?refresh="+df(D), url, "i.redd.it", 0), "&.*", "")$