http://rpg-exploiters.shoq.net/forums/viewtopic.php?t=5162
I haven't played WOW in a long while but I assume this still works. Credit for this goes to tcl70 or whoever taught him.
It's a long post, so in summary, load up WPE Pro with WOW, start sniffing packets, and use a skill. Look for a packet with a length of 12, that should look like: xx xx xx xx xx xx DE 5A xx xx xx xx, where the "DE 5A" depends on what skill you use, and the rest of the packet does not matter in this instance. Once you have the data you need, set a filter with WPE to change the 7th/8th byte of the packet (which is the skill ID, DE 5A in this example) to the ID of the skill you want to use. Some very useful skill ID's:
F0 42 - transforn into Onyxia
24 5B - transform into Ragnaros
FF 4F - Armageddon (GM spell to kill everything in a large AOE)
05 00 - Death Touch (Instant kill of player, monster, npc etc)
9D 5D - Instant heal (Current HP²)
9D 14 - Evasion Skill
9C 5D - Critical Chance skill
22 22 - Learn the Use Mail Armor passive skill
C5 1B - Learn the Use Plate Armor passive skill
37 07 - Learn the Use 1H Swords passive skill
6F 3E - Learn the Use 2H Swords passive skill
After you've done that, click on the old skill which ID you sniffed and edited, and it will now use whatever skill you changed it to!
This also works with items. Buy a random cheap item from a vendor and sniff it's item ID (15th and 16th byte in the packet, instead of 7th and 8th) Set a filter to replace it the same way you did with skills, and you can literally buy any item in the server if you know its ID. Some good items:
77 45 - OMFG sword
07 00 - 1000 gold at the price of 2 copper (Price can be higher if server admin edited it)
C0 00 - A weapon that has a spell similar to "Armageddon", but with a larger AOE.
Many more useful ones I can't remember, there's a downloadable list of all item IDs floating around the net.
This exploit isn't all that new and is pretty easy to figure out, but even so, when I played WOW (a couple months ago) I didn't see anyone else using it.
THIS ONLY WORKS ON EMULATED SERVERS.