Okay then!
These are a bit complicated to explain since they're not a standard monster.
Island of War has a whole chapter explaining the rules that govern them. Rather than typing out the whole thing, I'll give an outline and quote the relevant bits as we need them.
A guardian juggernaut is a 30 foot tall totem statue that can be turned into a remote-controlled magical mecha. In
Island of War they are created by a "barbaric" race of humans called Knorr to defend their clan. There are three types of Guardian Juggernaut. Wood, Stone and Wicker.
To animate the juggernaut, a cleric casts a special spell upon the pilot (called a "helmsman"), who must stand within a "circle of control" circle inside a ritual tent. The helmsman's consciousness then joins with the juggernaut and animates it, causing the juggernaut to move in synchrony with the helmsman's.
The resulting monster combines the helmsman's combat statistics with its own. i.e. a Wooden Juggernaut has Hit Dice of 5d10 which it combines with the helmsman's HD. It has a few special attacks derived from its size - sweeping away enemies or crushing them underfoot.
A guardian juggernaut can be equipped with magic items by storing them inside the statue and having the helmsman wield specially carved wooden duplicates of the item from inside the "circle of control".