Chryssalids are terrifying. If you are familiar with the first game, they are the reasons why you fail all those Terror missions. This time around, these foul alien species are neutered. They are not as terrifying as their first incarnation. Nothing really changed, they are the same as before, but even though technically in XCOM 2, you have less resources, you have more counter-skills against these menacing critters.
What they do is the usual, run across the map and striking damage to your soldiers. They still have the “Chrysallid Poison” that deals damage every turn and if a unit dies from it (whether an ally or not) they will turn into a cocoon. The Cocoon then have three Chyrsallids coming out of it if left unchecked for three turns.
Chrysallids Burrow under the earth. They will emerge as soon as a nearby unit is passing through. By the time you are about to meet and greet these creatures, you must already have Psi Operatives to mind-control anything or a hacking Specialist in order to force them to get out of their lairs and fight it out.
IMPORTANT: NEVER MIND-CONTROL CHRYSALLIDS AS LAID DOWN IN THE Psi Operative SECTION.