2 Fire Pit Traps that opens and flames rise when approached and whatever troops are near it falls into it...no amount...just all the troops near these traps falls in...including Barb King and Archer Queen. It's about where to place them that you have to consider. The cost would be around 4 million gold per trap and takes about 7 to 10 days to build. Unlocked at Townhall 8.
Not a bad idea, I'd say start with a spike pit first to be able to allow more upgrades to a fire pit then a lava pit. Have a limit of say 5 troops for the spike pit, 10 for a fire pit, then 15 for a lava pit. Once you get to the lava pit you can get the Arch Queen or the Bar King.