Tomb angel is legit great idea! Always keep forgeting that her ult doesn't care about enemy level.
Okay, gonna try to build the angel and the thief. Haven't run into a single Cyan level 150 for a bit now. My problem is I don't have any Cyan heroes. I have 2 Orange+6, a few+5, and on down to purple+1. All my heroes are level 100 or higher.
you may find this thread useful then:computer enemy levels
I love tomb angel and i use her everyday and as kob and others said above a nice solution to spectral. If you have limited resources, I actually recommend working on Thief first because she is helpful In so many areas of the game and often is a solution to the meta. It is nice that tomb angel is not tasty though.