I think the Dash might be a little over powered. Currently Dash can be used as many times as the user likes as long as Will Power is available. It’s possible to Dash across the full map and flank the enemies. Killing enemies provides more Will Power and the cycle continues.
Possible solutions:
Yes I believe it is slightly iver powered. But once you meet the mindcontroling aliens it gets a bit Interresting.
Lower your willpower the higher change för mind control.
If there are many uses for willpower so dash wont get it all the it will be different.
Dash, on its own, isn’t too strong, I think, in its current iteration. Will Power recovery from kills isn’t enough (unless you’re dealing with extremely fragile alien configs) to allow you to cycle dashing and killing endlessly. In combination with other abilities (and a shotgun!) it is definitely way too strong (at least at certain stages of the game - further in than I am it might be a necessary evil). Another alternative solution to the unending kill chain could be lowering the will recovery from kill.
At present, if you can’t kill an alien in one attack, you’re losing on Action Points and Will Points (unless the alien returns 4 or more will) OR if the alien doesn’t refund more than 1 Will Point you’re slowly losing Will Points.
At present, many tankier Triton and Arthron configurations can’t be killed in one attack by any weapon short of a Hel Cannon or a Shotgun. If you didn’t have a shotgun and were faced with these tankier variants using decent weaponry, 15-20 at a time, the skill combo would be strong but not necessarily seem OP and could possibly even be necessary to have a fighting chance. Weaker variants able to be dispatched by even 2 handgun shots while offering 2-3 will points per kill really highlight how OP the combo is.
How many things are combined in making the combo OP really make it hard for me to agree to where the change needs to come to fix it. Of your proposed solutions, though…
Only being able to Dash OR use other willpower only skills would make most skills worthless in many situations, make Will Points as a resource much harder to use and is not a solution I like the sound of at all.
The other two are definitely avenues I would agree are worth exploring.
Well thought out post, thanks!
A cool down sounds like a good idea to me, you can balance any skill you like that way.
A solider dashing to a close by spot on the map seems feasible within combat, but a soldier dashing around the whole map shooting everything on it before anyone else has a chance to move is getting into new X-com style magic that I thought PP was going to avoid.
I think that simply limiting to once per turn would be enough. Dashing multiple times is unrealistic. Quick aim more than once is too.
Having a cooldown is annoying, if you have the willpower it makes no sense to have to wait.
In the end, if I’m not able to do that, I’ll resort to bunker my troops and spam overwatch.
And solution should be:
For some skill should be limit 1/turn, for other 2 times per turn. But it should do the trick. You start the new turn and you don’t have to remember about any cooldowns from previous turns (even if they would be displayed).
From what I understand there won’t be such enemies. If they mind control (like mindfragger) amount of willpower is irrelevant.
The sirens do mindcontroling - I think thats what they were called.
The female looking ones with tail.
I played in easy and they were all over the place.
I think they do… however capturing siren doesn’t count for ‘captrure alien with psionic power’
At actual game build assault class is mandatory even as seconary class.
Sniper,Berserk,Heavy need it combo dash + other skill.
What skills we most using now?
Propably in 3/4 cases will be dash killing spree wasnt matter what class soldiers we had it.
Seems something is already broken, making other skills less important, important only for “special situations”.
Quick Aim on a high willpower pistolero guy is also funny. 10 bullets in one turn? Why not. It’s like 500 damage in single turn of just one guy and it isn’t hard or expensive to build one.
Btw. Why Quick Aim gives bonus to accuracy? Shouldn’t it work oposite? Faster aim (less AP) but at cost of accuracy?
‘Marked for death’ and ‘rage burst’ killed a Ciron in one go with my sniper 
That was quick.
I think, dash is to good as well. Most time, i move in the first turn forward and hide my solders, on the second turn i use “dash” on 4 of my solders 2-4 times to go in a good position to kill 2 enemys with a shotgun and “dash” away. In most cases, 2/3 of the enemys are down with this tactic. A bit to easy, except the Aliens have a MG with “return-fire”.
A limit to use “dash” once feel good, or an additional cost of an action point could be better, i think.
@Larbo: Try to give your sniper the Hell Cannon, than you have “Damage Deluxe” 
I love my Hellcannon Sniper, he hit very much on nearly each range
Neat idea! Havent tried it yet but mine got extra accuracy as his personal trait so should be awesome.
Another possible limit could be to reduce the range of ‘dashes’ maybe it should be just a couple of tiles for each dash.