%5B%5D is escaped URL for , so the real values there are p and f, but wordpress requires the URL to be escaped.
You can specify as many forums as you want in a single URL, but only the top limit threads from those forums based on most recent post activity will be shown. Only forums that are visible to the public can be linked to this way.
You can also specify as many filters as you like, the filters will only be applied to forums they're relevant to.
Example; a KMS filter won't do anything to General Maple discussion and a News filter won't do anything to Extractions, but if you use those two filters along with the forums General Maple, Nexon Announcements and Extractions you'll only get back News updates from Announcements, KMS extractions and everything from general maple, ranked by most recent post and cut off at your limit.
You can create multiple RSS widgets covering different topics with different levels of filtering.
*Note this is not a standard RSS feed and it is not recommend that users "subscribe" to it as the results are not incremental, it'll continue to change and rearrange everytime a thread receives a new post so the same material will be presented in a different order over and over, instead of new stuff arriving in a traditional RSS.
**Also note by default wordpress only refreshes an RSS item every 12 hours, so even though the URL will have the most recent info, your blog may not, if you've only got the default RSS plugin and can not set your own refresh interval.
JMS Extractions & Patches
MapleStory Announcements, everything but news, and facebook/twitter.
To answer a question I keep getting; Yes this works for Blogger, Blogspot, Typepad and most other services that allow you to include an RSS feed. The update delay on them will probably vary from service to service.