This is a fun ditty of a parody based on The Muppets song "Mahna Mahna." The lyrics the undead dude is singing are leet-speak words from World of Warcraft. I'll translate below the video. The song itself ends around 2:31; the rest is just the credits and rambly vocals in the background.
ROFLMAO-Rolling on floor laughing my a** off. (most people should know this by now)
PWN-Leet-spelling for "Own" as in "I totally owned that dude." A statement of superiority right after easily beating their opponent in battle.
n00b-New player, usually being derided for some clueless action or question.
UBER L33T HAX-Extremely good elite hack/cheat code. (yes, a double positive, for emphasis)
Pr0n-(I had to look this one up.) A deliberate misspelling of "porn" to get around language filters, sometimes for legitimate purposes in message groups, not just to be perverse.
WTG-Way to go. A standard commendation.
FTW-For the win. Congratulatory or boasting comment.
ROXORZ BOXORZ-(sorry, can't tell you, never seen it before this song)
OMG-Oh my God/gosh (depending on your upbringing)
HAX-A hack or cheat code for something.
L33T HAX WTG-"Super elite cheat code, way to go!"
PWN NOOBS FTW- Dominate new/inexperienced players for the win.
G2G-Good to go (off to the dungeon, to the raid, to kill horde/alliance in their own city)
C U L8TR-See you later.
LFG BRD-Looking for group to Blackrock Depths (a dungeon)
UBRS-Upper Blackrock Spire (raid level dungeon)
DM-Dire Maul (dungeon)
ZG-Zul Gurub (dungeon)
MC-Molton Core (raid dungeon)