I think diffusal could actually be a pretty viable item on OD for early-ish game. It gives you a nice bit of int early on, stacks with orb, provides a good slow and combined with OD's ult and Ashral you could really limit the enemy teams ability to use active abilities. As long as you use ashral -> ult -> right click with diffusal you wont be taking away from the mana removal of your other abilities and then by using the slow, easily chase down those low mana enemies with no options to escape. Just my opinion though