at the start of act two, chose ether beast or undead decks - from the photo i started undead. there are only a few cards you need to do this trick. First play the game as you see fit untill you unlock the age tower, i recommend doing the undead area first as they give you packs and gives you a better chance. once you unlock the mage tower head on up to the 2nd floor and fight against the training dummy. as far as i know its the only one that you can fight repeatedly for this trick and foils.

THE CARDS YOU NEED WITH OUROBOROS
1. Pharaoh's pet - 0/1 cost 6 bones. This is a rare undead card but it does have infinite sacrifice as well as goats offering
2. Necromancer (s) - 1/2 at the cost of 3 bones. This is a MUST have card to do this when a card is destroyed my sacrifice/damage/or a effect it triggers a second death effect
3. some cheap free cards to build up at least 9 bones (12 if you run 2 necromancers)

THE TRICK TO IT....
1. fight target dummy normally but dont destroy anything - summon what ever free cost card you have and HIT it with the hammer, continue doing this untill you have the bones you need and you are down to ONE card in your deck (if unlucky draw last card and go to next step)

2. Place the Pharaohs pet next to a open spawn to spawn ouroboros, fill the last two spots with necromancer (s)

3. Summon Ouroboros using the PET then hit him with a hammer and watch you necromancers create multiple copy's - each of them gaining a power increase - repeat this step untill you are sure you are satisfied and enjoy your new one shot - over kill creature :)