Best way I can think of is to catch the enemy as their doing baron, Flash into the baron pit and do carpet damage, And have the rest of your team keep the enemy in the pit as you channel your ult during Deaths defile. Though Realistically if you can just get some assists from that ability it's enough.
It's difficult to Just kill someone typically because Invulnerability, spell shields, or Zonya's can completely counter it. Though if You want the enemy to Insta give, make sure to go Hyper late game build. (I typically build Tear RoA)