First usage received warning of too many errors and suggested disabling addons. I did not disable, and tried it anyway. Result was it accepted the name to search for, but did not recognize the rare when it appeared. I tried with a normal mob name and it did not recognize it either.

Any way to TEST it's working properly? Eg. go to a specific place and scan for a specific mob?

This can never work. It's simply not possible with the classic api.

As someone pointed out the error for disallowed actions for TargetUnit only happens when the unit was targetable, so I was able to make it partially work. It's still very limited compared to vanilla.

• There is no 3d unit model.
• The found unit is not targeted.
• Clicking the button does not target it either (apparently targeting by name is not possible for addons, not even with secureactionbuttons)

(This is the retail branch btw)