FLIP: You can target Set cards on the field, equal to the number of "Subterror Behemoth" monsters you control; destroy them. You can only use this effect of "Subterror Behemoth Stygokraken" once per turn. When a face-up monster you control is flipped face-down, if you control no face-up monsters: You can Special Summon this card from your hand in Defense Position. Once per turn: You can change this card to face-down Defense Position.
Numbers of cards you destroy depend on the number of Subterror monsters you control.
All Subterror Behemoth monster have the shared Special Summoning condition of “When a face-up monster you control is flipped face-down, if you control no face-up monsters: You can Special Summon this card from your hand in Defense Position.” and the effect of flipping themselves face-down, so once you get one Subterror Behemoth on the field it would be easy to get more on the field. The problem is that all Subterror Behemoths are high-leveled monsters. Some like Subterror Behemoth Dragossuary and Subterror Behemoth Stygokraken can be summoned with only 1 tribute to get Subterror summonings going. You can also use Subterror Nemesis Warrior to Special Summon Subterror monsters.
This is the best support Subterrors have. The first and second effects hasten the activation of your Subterror’s effects. The third effect gives your monster a massive boost in stats, which could be enough to OTK your opponent. The fourth effect provides protection to your Subterrors while they activate their effects. All while being reusable because it sets itself back to your backrow after use.
The downside is you can only choose one of these effects per activation. But you can set multiple copies of this card and use all of them every turn.
Destroy Spell/Trap Cards
You can use Subterror Bememoth Stygokraken to destroy your own set cards to trigger other effects.
What am I doing wrong?
I flipped this monster but he didn’t destroy a single opponent card, I also had another
Subterror monster on my field
My opponent played Neos deck, and nothing that could negate the effect