Mini Tyrael

Where does it come from and how hard is it to get?
Tyrael's Hilt comes from the Paris Worldwide Invitation (WWI) 2008 goody bag.
Rarity: One per visitor to WWI 2008
Quantity: Speculated to be a print run of 8,000.

How much would I expect to pay for one off eBay or similar?
According to http://www.wowtcgloot.com/tyraels_hilt.htm (most information sourced from there), the lowest Buy It Now price starts around $700 USD upwards to $2000 USD. The price should remain steady and higher than the BlizzCon murloc items as it has the extra appeal the Diablo genre.

Facts:
"Mini Tyrael" is the in-game name of the Non-Combat pet.
The pet is a miniature version of the Archangel Tyrael from Diablo 2.
Edward Cairn redeems for Horde on upper Trade Quarter, Undercity.
Ian Drake redeems for Alliance outside the Auction House in Trade District, Stormwind.
Useable at any level and therefore available for twinks.
I have the 25 digit loot code, now what?
All accounts from every region in the world use http://www.worldofwarcraft.com/misc/promotion.html to redeem any and all special loot. This webpage allows you to enter the 25 digit promotion code and also select the region and realm for the character that will receive the loot item.

Upon succcessfuly submitting the above information, you will be presented with an in-game code. Write this code down or print it out; you will need it to retrieve your item. Log into the game with the character that is to receive the item and travel to Undercity for Horde, or Stormwind for Alliance. Find your Tyrael representative (listed in "Facts" above). Ensure you have got bag space to hold the item otherwise the item will be sent directly to your mailbox.

Credit to Daldain for this information.

You get the code from the Blizzard WWI, if I'm right.

This pet is NOT TCG Loot. This pet comes from the Blizzard Worldwide Invitational which occured in 2008 in France. It is not available any longer, except through purchasing the giftcard from ebay or the likes.