Children of Yllia seem OP

I literally just lost three games in a row against the CoY that went off flawlessly to start with, but then the same tactics was used to kill my Champion, that simply being to run up with Natural Selection and screw over any single unit in combat with Born Killer. Not only that, but the current free champion for them actually pulled off a full team kill on me by use of Bloody Blades and Natural Selection (and an obscene amount of Criticals), all because he was able to do two attacks with a single activation. I personally find this obscenely overpowered, as the CoY practically get a free Offensive Stance without the downside of losing Parry, every time they attack. I understand the concept behind having a 'Born Killer' perk, but it just seems far too powerful for a passive that seems to come with every CoY unit. Just stating my opinion a bit, so I hope this gets the point across.

What setup are you using?

Wolfens was weakest faction in n propably all versions except two (0.10 and somewhere in 0.12.x where they had more units than most of factions) Now they are only much faster than other factions and only in term of game duration.

as for usefull tactic vs them - you didn't even mentioned your faction and hero but i can gues that you are playing lions with archer hero or ram with Kain - becouse this two heroes are weakest/hardest to play against wolfens (imo Kain needs slight buff <especially his order looks weak - or combo use only> or cost decrease).

For RAM - try to use more skellys supported with puppets
fro Alahan - well - you needs more defensive play or turtled hth company - becouse lions can be nice counter - but they need some luck. So mostly you must base on some little combos - and blocking Kelrys with full health units only.

(This isn't so much aimed at you as it is aimed at anyone reading)

You need to watch what buffs the wolfen player is giving out as well. They have a number of buffs to help them survive longer and many players don't have the experience of what these are and do. A Wolfen Enchanter has two buffs that he can cast as many times as he has mana in a single turn. Ring of Ice: 50% chance to negate arrows fired at the unit for 2 turns. Ring of Mist: 50% chance to negate enemy magic casted on the unit for 2 turns. Whilst they have these effects going you should be looking at other targets with units whose attacks might be negated, killing the opponent's Enchanter will hurt him alot if you can manage it.

Then theres Mortal Insolence, when this is activated the unit using it is more than invincible for the turn. Every attack directed at him will be negated and for every attack directed at him he will recover health. Any attacks thrown at him is going to be counter productive. If your not sure if these effects have been activated you can check your opponent's Wolfen using your mouse.

the current free champion for them actually pulled off a full team kill on me by use of Bloody Blades and Natural Selection (and an obscene amount of Criticals)

This is nice exaggeration, as champions cannot be given orders.......

Kains Exhausting spell works magic against CoY, Ive been destroying their free champion using that, with the human faction Ive been using the hinder movement skill on rangers to take really control them

I just pick a unit and deal damage until it is dead. The Wolves have such low unit counts that it very quickly becomes telling.