As someone whom been playtesting the subterrors here is what they need in the last set Maximum Crisis to make them playable within there own archetypes:
1st: they need no tribute normal summon monster that can flip itself facedown (or any of them) in order to activate the swarm effect of the behemoths
2nd: they need a continuous trap card that that works similiar to "Ghostrick-Go-Round" that can be done during either players turn to either flip a subterror facedown or face up but works specifically for subterrors
3rd: they probably need a behemoth (or a continuous spell or trap) that when flipped/activated gives all subterror monsters (or just behemoths) piercing damage to synergy with Ultramafus and the new Clash of the Subterrors (which it could be either the level 11 or 8 subterror monster that we're missing since that's the levels that we're currently missing)
4th: is the easiest one is a spell card that can search out a subterror card outside the field spell since nemesis archer is the ace card in the archetype to make it go off
One errata i wish that they did was to make stalagmo use it's "destiny draw" effect on any subterror card to make borrowing a better card and have a way to send that to the graveyard as well.
Overall the archetype is actually pretty good idea but if we can at least get piercing/ and a "ghostrick-go-round" then the archetype will be playable and honestly a threat.
side note: i copy and pasted this from my comment from facebook so sorry if you can't read this well but i think we can all agree that these are what subterrors need in order to be playable and a suprise.
Also has anyone tried out Raindeen the Eidolan Beast in the deck as an instant fusion target? To those whom haven't it's amazing and instant fusion is a definite 3 of