Purple People Eater is the only proper choice for a species here. Anything else like Alien or some gibberish, nonsynergistic name is clearly invalid.
Devourer and Relentless work for me, although I'd rather see him in Valkrill rather than Utgar if we're going for the black hole theme rather than an eldritch one. It better matches the mass consummation in my opinion, and Utgar already has plenty of units on his own (with other likely candidates like Ob Nixilus in this set).
If we do want to present this guy as some Lovecraftian horror, then I could see him in Utgar instead to match the Mindflayers thematically. The main difference to my knowledge is whether he'll be able to be used in Ornak hodgepodges or not, which although fun, typically aren't the most competitive of armies.