I'd probably cap the Split ability at one iteration. At most, I'd allow "permanent ability score modifier" instances of itself in total; probably either Con, Cha, or Wis.

Query: can a Split Protean Scourge assist itself?


If we ignore Split, it's a respectable +0, and Split is definitely due a DM warning, so +0* as is.

I agree that it definitely feels more like it was supposed to be some kind of evil outsider. That or some kind of enhanced-doppleganger type deal.