Who Let Kaldr Out?
As Skadi kill 3 or more enemy gods in a match with Kaldr.
Kaldr is a pretty important part of Skadi. How you do this is by using her ability "Rune of the Hunt" to call Kaldr to hunt after an enemy. You have to be in a pretty reasonable range of the targer, and the ability is on a somewhat low cooldown. Kaldr will not stop chasing after them unless he is attacked 5 times. A good combo to do is to slow down the enemy using permafrost letting Kaldr get more hits on them.
Overall this is not a hard achievement to get, and can be achieved by playing the game.