The Pentagon. Produces almost unbeatable troops, but every time you start a battle half your coins, supplies and medals disappear. Once you're down to 1 of any of those resources you can't start any battles until you have at least 2 of each. Within that framework, also allows unlimited battles in GBG and PVP Arena, but each time you start with one less unit until you're down to one unit, and then you start again at 8, but only after winning a battle with that one unit.