vasik
The two criteria above must be met, and both of them:
<SpellPoints2>1</SpellPoints2>
<CreatureTown>TOWN_INFERNO</CreatureTown>
The number of gate openings is easily adjusted with this parameter. If it's two, it will be able to open twice.
I checked just in case — ABILITY_DEMONIC, its absence won't prevent a creature from opening gates if the town type is Inferno and SpellPoints2 is available. (but it is important for Holy Word and Fire Wave)
Maybe you'll buff your creatures that are both neutrals and demons?))))
Just for fun, I'll also check whether an 8th-level incubus will open gates under the Pendant of Mastery on a demon.
They can. If you make demonic neutrals properly, with the right race and spell points, even 8th-level ones with the pendant will be able to do what a demon needs to do))
Including balgors and antichrists 
Still, they will differ slightly in description — for the Nunkugha, when opening a creature, the town is not "Unknown" but Inferno. For incubi — "Unknown". I think it's because the creature is 8th level and has the "Unknown" tag in the description. As it should be, gating works for incubi with the Pendant of Mastery (4th gating, doesn't work without the pendant, as it should) and with the correct creature file description.