I would say its a big falkow grim, a really good one actually. I wish to have one too. I saw some situations where it would have been particulary devasting. I regard it as the only good anti big card beside leviathan (a good big player other then falkow possess plenty low lvl cards to spam them if he suspect legyre thus I exclude him from that, he is on a border of uselessness and only hurts unexperienced/ ppl who do not expect him/dont know him at all
you don't mind to loose sp or see your units dying as long you have more sp on your field then your opponent and gain the extreme sp advantage you so desperately need for big falkow to make it work. Also it is great in some situations like against an endgame zugateroza, dalos or some other crazy sp skills (unfortunatelly its not a solution against shvara....)
Maybe it fits also in some other decks with volfied SS but yeah for a rush 4sp is a bit much... nad mid has better options to use 4 sp as they can be more aggro.
Also it unfortunatelly absolutly oppose the usage of durendal...
now that i think of it could also fit to control decks like dio/mystere, in case your opponent start to skip a lot to gain the sp for unit + grim spam move.