I have just re-discovered the Apocalypse: re-loaded strategic asset for Tzeentch. It's called the Mirage of Tzeentch, and in essence allows you to take control of any opposing unit for one shooting phase (so long as it is within a certain range). Yep - that even applies to titans, super-heavies and the like.
Having re-reviewed it, I am shocked (once again!) what a powerful strategic asset this is. If Lash of Submission was game-breaking for allowing you to move your opponent's miniatures, then this piece of trickery is truly impressive. Unlike the Changling's ability, there is no second chance to decide not to fire a certain unit. The effect goes off, and that is the end of the story. Your targeted titan does what you want it to for an entire shooting phase!
If apocalypse is ever reviewed (or indeed, re-written for the next edition of Warhammer 40,000), I wouldn't be surprised to see this power change. That got me thinking: is there anything else in apocalypse that folks think should change in a re-writing in the future? Comments welcome!