SMITE

As Olorun, with a single ability use, kill two enemies within Sanctified Field.

Sanctified Field is Olorun's ultimate ability. You create a relatively large rectangle in front of you. All enemies caught in this have all types of speed, movement and attack reduced by 40% and you gain a 30% increase of all of those things. When you activate you ultimate, you need to get a double kill with another ability while in the confines of your ultimate. The best ability for this is probably your 2 once it's fully stacked (it's stacked by activating it once and hitting enemies, including minions and jungle monsters, and then pressing your 2 again to fire off some shots at the targeter on the ground) or your 3 (which knocks people up in a small area around you as does more damage).

So you'll to have at least half-charged your 2, then you'll want to activate your ultimate, preferably on two or more low health enemies. Head towards them and activate your 3, which knocks them slowly into the air (your ult amplifies the slow). Activate your 2, aim then activate it again to send a load of projectiles at the targeter on the ground, preferably at the enemies you're trying to kill. If you get a double kill with either the 3 or the 2, you'll pop this achievement. The double kill must come from the same ability (it can't be one kill from your 3 and one kill from your 2).

With thanks to NutriWhip and Bulk Galaxy, you can get this simply by using your 2 to increase your attack speed while inside your ultimate, without having to use the projectiles.

The build I had when I popped this was Demonic Grip, Bancroft's Talon, Telkhines Ring, Rod of Tahuti, Shaman's Ring and Spear of Desolation (and then an elixir of speed).

Best attempted in Arena, as that's where people group up the most, but Conquest would also work, as you can trap enemies in your ultimate more easily using walls.