SMITE

This is for healing at least three allies at the same time as killing at least one enemy with Isis' ultimate ability, Circle of Protection, which is exactly what it sounds like (a big circle). Basically the way it works is, the more damage dealt within her ultimate, the more damage to enemies and healing to allies it will do when you detonate it. You can detonate it whenever you want by clicking whatever button you use for your ultimate (depends on your control scheme, if you use standard controls) once it's out on the ground.

So basically once you have an enemy (or enemies) in the circle, and enough allies, try to gauge when you should detonate it it to secure the kill. You can roughly see how "powered up" the ultimate is by seeing how filled the bar in the center of her ultimate is. You can see a clip of me unlocking the achievement below (the award pops up in the bottom right corner of the screen).

"As Isis, heal three or more teammates and kill an enemy God using a single Circle of Protection".

Circle of Protection is Isis' fourth ability (ultimate). It works as a large, ground area marker. Any damage dealt within the radius powers up the staff at the center, which causes it to deal increased damage to enemies and healing to allies upon detonation. Charging up will help you guarantee the kill, but the best way to do this is to target a weaker player and detonate it early/immediately to make sure you kill them.

Playing in a party will help coordinate your teammates into getting into the circle, although experienced players will do so automatically to get the heal off. Having an Odin on your team may also help, as his ultimate can trap enemies in, preventing them from escaping whilst you charge the ability.