Its a very logical requirement. Activating hero flash at 10th turn lets you summon a normal hero from your deck. It would be nice if there still were normal hero monsters in your deck at that moment. Very easy requirement to meet.
I wonder when are we going to get an actual copy of Emergency Call.....
Pretty oddball skill and mostly just a gimmick, it does add cards for free but also requires running 4 DIFFERENTLY NAMEd normal E Heroes. Best used alongside some copies of Neos together with Grandmerge.