It’s been revealed in a magazine. Avoid reading further if you wish to avoid dreaded spoilers.

He uses ‘eerie’/’strange’ looking monsters called 地獄螺戦鬼（ヘルリックス）. The Kanji reads “Hell Spiral Battle Ogre”, but reads as “Hellix”. Not Helix, like SPYRAL Double Helix, but “Hellix”.

This monster from Episode 23’s Preview is presumably a member of the “Hellix” theme.