can you play this card over and already corruptud unit?

Another situation: my oponent has in table only 1 unit, Daemon prince, and plays seductive delusion over his unit to dealt damage to another unit of my own, i respond with sacrifice to khaine, will my unit die?

This card won't do anything if the unit you target is already corrupted. Because it says "Then…", the first effect has to occur before the second. In this case, that unit has to be corrupted first, then it will deal damage equal to its power.

The second part of your question is a little more difficult. I would say yes, your unit will still die. The reason I say that is because the effect of dealing damage equal to the power will exist regardless of what happens to the source of the effect once it has met its trigger conditions and the action taken.

I have been wrong before, woefully, so hopefully someone else chimes in.

You can play that card on already corrupted unit, but there will be no damage

I think "SD" will fail because "Corrupt that unit" is not an additional cost but it is a part of the effect to be executed, when the effect will be resolve.

Resolving first "StK" which eliminates the "DP" can not allow to solve the first part of the effect that requires "Corrupt that unit" in order to execute the second part, "Then" requirement.

Horatius said:

Ya, I'm not 100% sure either way. I think you might be more correct than I was.

Horatius said:

This is correct.  As you resolve, he will have to sacrifice the DP for StK, then he will resolve SD and be unable to corrupt the DP (since its gone), meaning the part after "Then" doesn't happen.