What would the CR change be, if any, if I changed the Babau demons', in L25, abilities to remove dispel magic and add greater invisibility? This "super stealthy assassin" feels better with this to me. I don't discount dispel magic. I love the spell actually but with the description in the PRD I kept looking for their invisibility ability and couldn't find it. :P
Unless dispel magic is inherent in how they operate I don't see why they have it. I would also probably take away their spears.
They have Stealth +22, they don't need Invisibility :D.
Do...Do you want to kill your party that badly?
My group missed those two rooms and frankly I'm glad because I think some serious blood could've been spilt. They are tough customers, and three of them gives a fair bit of extra damage as they flank and such.
Giving them greater invisibility, unless your enitre group has some easy invisibility remedies (in which case you're really not adding much to the encounter by doing this), is outright mean.
At least, that's my gut reaction. I don't know your party, don't know how much ease they kill things with. If this is what you need to challenge them, and your players aren't going to throw books at your head for sending three nasty beasties at them and giving them greater invisibility, go for it.