I have a friend who runs a wolf army with what were at first 3 wolf cav with 3 shields and a hammer, and later 2 separate guys with hammer and shields. These 2 tear my nids apart. The trio killed 2 trygons, a tervigon, and 30 ish gaunts before I Finally stopped them. 6 3+ wounds in the squad, I had to inflict something around 45 to kill them, and they should die after 18. The solo guys are pretty bad too. I have, on three occasions charged one of them with 20 gargoyles with toxin sacs and adrenal glands. Second time it died, first and third time that wolf cav ate all my gargoyles and kept going.
It has nothing to do with the unit strategically or being cheesy, its just the worst combination of luck.