Well what happens when you try to cram too many aliens into a game? You get a Reaper/Chryssalid. Fine. In XCOM it worked fairly well. An alien who was quadrupedal and spawned from a zombie. Yet in XCOM 2 "no tagline needed". The Chryssalids are now utter shit? I mean they aren't a threat, by the time you encounter them they become an annoying inconvenience. What they should haved used, since they are totally stealing from Apocalypse is the Popper. An alien that screams its way past cover and locks you in avoiding danger with the intention of mindless destruction. Sounds good to me. The hardest alien to kill in Xcom 2 is simple, it's killing the aliens that harm the entire squad with only one power. Once that happens the rest is a breeze.