FOE - IOSYS - Etrian Odyssey - DS

First off, IOSYS is a doujin group that does music arrangements for games and often make a promotional flash video to go along with one of the songs of the CD.  This particular video/arrangement is based off the FOE Battle music from Etrian Odyssey for the DS which is being released next month (English, Japanese version has been out a while).  The FOE system is one of the features of the game where certain triggers could cause FOE encounters, which are like semi-boss fights.  The video basically makes fun of it saying anything you do will probably trigger an FOE and kill your entire party.  Yeah, the game's supposed to be old school hard.

http://iosys.tv/flash/IOSYS_foe.swf

Towards the end they reference a few popular memes, some of which are based on their previous flash videos, which BTW, are here:

http://iojacket.hp.infoseek.co.jp/IOSYS_tohootomebayashi_loving.swf (their most famous video)
http://iojacket.hp.infoseek.co.jp/IOSYS_tohotsukitoro.swf (a later video that's also pretty popular)
http://iojacket.hp.infoseek.co.jp/IOSYS_tohootomebayashi.swf (from the same album as the Marisa video)
http://iojacket.hp.infoseek.co.jp/IOSYS_tohokazakuraen.swf (their first video)

The "Saitama Saitama" reference is a reference from the 2ch messageboard, the "Erin Erin" reference is a meme from the Touhou games (the 4 videos above), the "gossun" reference is from their Marisa video, and the "doman seman" reference is from a merged video of their Marisa video and some Onmyouji video and became extremely popular on http://www.nicovideo.jp (a site that lets users overlay scrolling text on videos from places like Youtube, often with hilarious results).  You can't see the video unless you're registered there, but the Youtube version sans text can be found at http://www.youtube.com/watch?v=MU9Ui4807r4

Oh, did I mention their Marisa video is really popular? :p http://video.google.com/videoplay?docid=-3822956513969579461&hl=en

BTW, for the "Erin" reference, http://www.youtube.com/watch?v=cMPB8iVK20Q. This is the group that started it with their arrangement for the same Touhou game.  Yes that's a bunch of people gathered together for a live performance of a fan arrangement of an indie $10 game series made by ONE person. That's how popular it is.  It's more can be said for most games out there, both indie and commercial.

Edit: Missed a video, thanks Benny1!