Wraith - Possible to select spell effect?

The Wraith’s spell description says the following: “Steal X life from an enemy, OR steal their mana.” Can you manually select which one of these effect will occur or is it down to RNG?

If it is the former, can you explain how to do so? I tried clicking on the life/mana icon of the enemy but it does nothing.

If it is the latter, I guess it is done to balance out the troop, even if it might be frustrating to the player… It also isn’t very clear that the effect that will apply is down to luck, especially to a newbie like me.

It’s random, but yet it is surely annoying when he steals mana over and over…

Thanks for the quick reply!

Yes, I had the situation where it would steal the mana instead of just outright killing the enemy, or vice-versa where I can’t kill the enemy but I would like to deny his mana pool…