Cast 2nd abillity..."Invalid Target"

[BL4CKN0ISE]

Why is this a thing? I understand why it wouldn't work on a boss, but I don't understand why Garuda's 2 doesn't work on other enemy types. What happened to just having shorter duration on certain units? Why do they need to be considered an "invalid target". I also would love some consistency with this. Nidus can still CC everything in the game. 

I'm also getting tired of instant kill abilities not working the way they're supposed to work. Some units just completely ignore the 40% health threshold for Dread Mirror. This is the same problem Revenant has with certain units and his insta-kill ability. If these are bugs, please fix. If not, please reconsider how you're thinking about them. Thanks.