Deflect

If a champion has an ability which triggers when damage is dealt (such as Rend, Stun...), and its attack damage is diverted to another champion, the effects will be transferred to that other champion.

For example, if Champion A has Chill and attacks B, who deflects the damage to champion C, then champion C will become Chilled instead of champion B. (This makes sense, because the damage to champion C is still because of champion A.)

Make sure the ability requires damage. Some abilities (such as Soulstrike or Sunder) only require the attack to be successful (not miss). It doesn't matter if the damage is dealt elsewhere as long as the attack didn't miss.