Diffusal Blade

Nothing works to completely counter the item since its' 8 second Purge cooldown is so quick they can just counter every Repel you cast. An Octarine Core will help keep you casting so that you can keep Repel active for a little longer and use more of their Purge charges, but with 16 charges available on upgrade, it's a difficult item to hope they just waste and discard. Always keep your distance from a Diffusal Blade carrier, if they are an Agility hero you could find yourself without enough mana to cast your spells in only a few seconds. Give your team a heads up that someone has a Diffusal Blade and tell them to target that hero first so you can neutralize the threat as soon as possible.If the enemy targets you with the Diffusal Blade because you self-cast Repel, one strategy i've worked with is a Manta Style. It gives you a 2/3 chance to dodge the Purge cast and then a 50-50 if they took out an illusion with one of the charges. On occasion i've ran out of sight, cast Repel on the illusion, and ran back in just to watch them Purge the 2nd illusion for giggles. If you initiate for your team or if you find yourself closer to the front line during teamfights, one strategy I have found effective is to cast Repel on an illusion and send it in alone to draw a Purge cast and a few enemy stuns just prior to initiating.When I get lucky, I draw a Purge for the illusion's Repel, re-cast Repel on the illusion from behind, then I get 2nd purge on the 2nd Repel cast, and a 3rd Purge to dispel the illusion, or a stun/disable cast from the enemy team. That's 2-possibly-3 Purge cast charges, leaving a Diffusal Blade that much closer to depleted, or a stun/disable applied to an illusion which helps right before a teamfight. This is my current favorite strategy to keep the enemy confused and to remove some of the threat of a Diffusal Blade.