If this idea interests you in anyway, it could be unbalanced or it could be balanced depending on what you set for it.
Thanatos, Sword of the North-Not dropable or sellable. Sword imbued with great and chilling power. The user of the sword can place down 4 wards in an area. These wards are not visible to anybody, and cannot be destroyed. When these 4 wards are placed in any arrangment the user wants, the hero can enter that area and unleash a mighty, slowing and damaging AOE in the region where the wards were placed around. This AOE destroys the wards in the proccess, forcing the user to place the wards down again, but other than that have no negative effect on the user. This may seem unbalanced, but that is why this other item is introduced.
Pyrokhaos (Flames Chaos)- Although it has no special damaging besides an attack boost and a splash attack, it was forged to counter Thanatos. When the hero carrying this sword approaches a Frost Ward, the ward becomes visible to the user. When a ward is destroyed by Pyrokhaos, it does a good 30-35% damage to the hero carrying Thanatos (damage can be adjusted). When the hero carrying Thanatos is killed, Thanatos detonates in a huge frost nova damaging allied units. Other debuffs may be added to Pyrokhaos if you believe it is neccesary.
Hope this gives you an idea or is helpful.
~Asomath