The IT'S ALIVE teaser leads me to believe it's one of two possible conclusions:
Option 1 is that this is the exclamation of someone who has done their absolute damnedest to try and kill something, and thought they did so, but failed. This would definitely fit in with the theory that the new champ is a darkin, knowing what we do about them. That said...
Option 2 is the far more well known application of the phrase, which is to say it's the exclamation of someone, probably of the mad scientist (or mad sorcerer) variety, who has just brought something to life a la Frankenstein. I find this to be more likely, since a) it is the more common use of the phrase and b) ever since Urgot's rework, league hasn't had a Frankenstein-esque champ.