Anarchax is currently the most powerful heavy weapon in Infinity Blade II, and has the highest raw damage rating out of all weapons. It has +1500 attack. Oddly though, it is not the the most expensive Heavy Weapon. It is wielded by the Horned Chieftain. It can only be unlocked by starting a NewGame+, or occasionally through rare prize wheels. It can also be taken from a Large Chest and can be easily obtained with the Vile set since it has "+30 Drop Rare Items" bonus.
Anarchax is a limited heavy weapon in Infinity Blade III. It was awarded exclusively to the 32 winners of the Shattering the Dark Mirror Aegis Tournament, and cannot be legitimately obtained by anyone who did not receive it through the event.