Discord had started an infection because he tried to revive Fluttershy. The infected are called the Grieved. Ponies have taken shelter in Chrysalis’ castle. The Changelings get to feast off ponies love. The Grieved also go after love but if they can’t sense it they’ll go away. Working with Chrysalis has given the ponies the safety they needed. Chrysalis does taunt the Princesses so that’s another bonus for her at least.