"5 - Sabretooth, Savage Killer

Whenever a character causes breakthrough, Sabretooth cannot be stunned while attacking this turn. "

So if he causes breakthrough, would he get stunned? I'm not sure on the sequence of events of when breakthrough happens, when the stun happens, etc....

Thanks!

Correct also if your opponent's character causes breakthrough while attacking (and somehow you still have toothe to attack with)

wow that didn't help at all. No, sabretooth does not keep himself from getting stunned if he's the one causing breakthrough. The breakthrough he deals happens after he's already stuns

Just to clarify, I was thinking of a scenario where Sabretooth would normally stun back. Like I Flying Kick Sabretooth and send him into Wonder Man.

That would not work because in the stunback scenario Sabretooth is not attacking but defending.
Here is the explanation of Sabretooth's from UDE FAQ for X-Men

Sabretooth’s power triggers whenever a character controlled by any player causes breakthrough. If Sabretooth himself causes breakthrough, his triggered effect doesn't go on the chain until after that attack concludes, so it won't save him from becoming stunned in that attack (but will save him if he manages to attack again that turn).

Fascinating have to check the FAQ more often, I assumed it checked at attack resolution wrap-up when you would compare totals / stun / deal break through. Thank you.