Further insight :
When it says 30+ undead for skill
It means 30 lvl= 1 point in skill
60= 2 points
90 =3 points
So if u did this u would always own
Use dark bat and use all heros purple lvl 60 for 240 lvl which will be 8 points in final skill .... 400% heal from that damage per hit of that skill ..... 
U deal way more than u could ever as a character when that hits and u always full heal .... If u could put them all like that