It only wishes death to intruders of it's domain, so it will charge on you with all haste.
The most powerful creature with normal spawn since the Christmas Update 2006. In the official website it says that it can slash the head of a Dragon with one hit, while fighting back a half-dozen of other Dragons, which suggests attacks of 1000+ and very high defense. It is also known as the creature (with a normal spawn) with the highest HP.
The Juggernaut's strategy is fairly easy. All that is needed is a blocker with very high skills, health over 2500, and a mage to heal the blocker with UH or a druid with exura sio (Heal Friend Spell), while the rest of party attacks the Juggernaut with SD or energy based spells. They are found in proximity of Furies, Destroyers and Demons, so you can't hunt only Juggernauts. The best place to hunt plain Juggernauts would be the single spawn. They are also very fast, but since they have no wave attacks you can let the blocker lure them to a small 1sqm wide bridge in the Apocalypse's throne room, and just let the shooters attack it with SDs. The Juggernaut's boss is Massacre also located in Apocalypse's throne room.